"(With) a grain of salt", (or "a pinch of salt") is an idiom of the English language, which means to view something with skepticism, or to not take it literally.
BoC began 2016 by breaking their silence after "Tomorrow's Harvest" by releasing two new remixes one month apart from each other, Mr Mistake by NEVERMEN and Sisters by Odd Nosdam. The latter was accompanied by a video  which was formally released on February 22nd. This led to some speculation that some new material could be in the works.
After a few months passed, they recaptured the attention of their fanbase with an innocuous post to their generally dormant social media accounts on June 6th, 2016, linking to an existing fan made video for "Macquarie Ridge". A month later, on July 7th they retweeted another fan video of the "Broken Drum by Beck" remix that had been posted to Twitter on July 2nd.
They tweeted once again, this time a Youtube link to "Peacock Tail" on July 31st. The last post raised some uncertainty as to whether they would continue posting in a 6/6, 7/7, 8/8 type frequency.
Around this same time, ASCAP entries for a release entitled "Harvest Ritual" and Untitled (Machinedrum reconstruction) were discovered , but quickly disappeared after they were noticed and the former subsequently waved off  as an old Tomorrow's Harvest related entry by someone  making their first (and still only) post on the Twoism (messageboard). After 8/8 came and went, the next known date of interest was 8/22 (the 20th anniversary of the system date on the Cosecha-transmisiones console) but this date also passed without incident.
With 8/8 and 22/8 eliminated as possibilities, what's the next date that would make sense for them to make another appearance out from the ether?
They finally posted a fan video for "Nothing Is Real" on August 24th which didn't seem to follow any type of previously speculated upon date related logic.
They posted again on October 14th, this time for the song "Left Side Drive".
Over the span of the few months described above, they had begun liking various fan posts on Twitter, seemingly at random, many of the fan posts including pleas for new material or involving the liking of tweets that included their own music. This activity slowed down as time went on, briefly peaking at 49 likes before dropping back down to 48 likes, before going up to 49 likes again in February 2017 - the original 49th liked post was deleted by its author, so keeping the tally set to 49 likes seemed important to them at this stage.
They posted a new fan video for "Open the Light" on December 8th, alongside a simultaneous heavy revamp of their Youtube channel playlists, which had been in need of some upkeep as by that time, as there were multiple broken or delisted videos from over the years. What was interesting about the "Open the Light" post is that it wasn't cross-posted to Facebook, the same as "Peacock Tail" back on July 31st. I feel that these omissions from their Facebook account weren't an accident but rather, those 2 entries were only relevant to a pattern that they were establishing at their Twitter account, but more on that in the Posting Details section.
Rather than a new release announcement at the end of the year, the Youtube video channel revamp seems to have joined the campaign midway to serve as a map of sorts, providing vague hints to assist in navigating the numeric trails being blazed at both their Facebook and Twitter accounts for those who were trying to pay attention. I'll go into more detail on that as the timeline continues to progress.
After the playlist revamp and the "Open the Light" posting on December 8th, they went silent for the rest of 2016.
BoC returned to Twitter on March 28th, 2017 with a posting of the "Dayvan Cowboy" video. Shortly before this (sometime within the several hours prior to the Dayvan Cowboy post) they deleted an old tweet from March 11th, 2012.
Now that the events have been summarized, it's time to get to the details. As described above, each social media network account seems to have its own unique pattern, but the same crucial end points. Twitter is the most plentiful (and therefore easiest to pick out a method to the madness) so it's best start to start there with a list of the dates and posts so far:
6/6 - Macquarie Ridge - 3:06 AM CET
7/7 - Retweet of Broken Drum from 7/2 - 12:19PM ET (original tweet)
31/7 - Peacock Tail (2005) - 5:25PM GMT
24/8 - Nothing is Real (2013) - 12:57PM UTC
14/10 - Left Side Drive (2006) - 3:11AM MT
8/12 - Open the Light (1998) - 8:57AM UTC
28/3 - Dayvan Cowboy (2005) - 6:56 MT
- The main pattern to follow for 2016 involved multiplying the date and month together for the posts when both numbers are divisible by 4. We add up to 24 in other even numbered months. We subtract down to 24 in odd numbered months, the odd months are also preceded by a retweet. For 2017, we may be multiplying in odd numbered months instead.
- "Macquarie Ridge" is unique (for now). I'm going to defer to Video Playlist entry 66 - Constants are Changing and say that we should subtract, not add or multiply these numbers.
- The other hint to multiply is when the timestamp ends in :57. The timestamp on the Cosecha console was 2:57 - potential nod to the number 70 2x(5x7)
- The multiplication sum halves with each subsequent step, while alternating with the added/subtracted 24s, and de-increments by 4 hours each time it happens. (12:57 -> 08:57 -> ??:??)
- The multiplication steps for 2016 included a number from the previous multiplication based step, and carries over the number to the next step (ie. 24 - 8 - 8 - 12) meaning that the month of the current tweet will be part of the subsequent tweet's date. ie. August 24th means the 8 carries to December, giving us December 8th, etc. As of 2017, the first post (28/3) indicates that we may be reversing last year's rules (84 instead of 48, multiplying in odd months instead of even)
- They specify the year of release for "Peacock Tail", "Nothing Is Real", "Left Side Drive" and "Open the Light" in the title of the respective tweets. If treated as two pairs, they are both separated by 8 years. A look back at their discography determines that 2001 and 2009 as the only other remaining pair of year that functions this way.
- Based on the rules above, omitting any retweets, the main numeric pattern for 2016 should be read like this:
6/6 - 0
31/7 - 24
24/8 - 192
14/10 - 24
8/12 - 96
These are the posts for 2017 so far. I believe that 2017 will function like a mirror of 2016. The first post indicates that we may be targeting divisors of 84 (as opposed to 48 last year) and multiplying in odd months instead of even:
28/3 - 84
All recent Twitter posts have specifically been part of this assumed large pattern, or have been related to promotion of a remix or physical release of some kind. That initial Broken Drum post didn't seem to make much sense in the scheme of things when it first came about, other than being a red herring that initially hinted toward a potentially more straightforward series of posts such as 6/6 7/7, 8/8, etc.
Going back to 2016, the Broken Drum retweet set up its own sub-pattern starting in July 2016. The original posting date (7/7) is obfuscated on Twitter because it's a retweet, but it was mentioned on the Twoism (messageboard)  on the day that it was first posted. This means that there were posts on 7/7, 31/7, and 24/8 - the commonality is that the posts were separated by 24 days each. The retweet approach seems as if it was intentional, to separate it from the main pattern and hide the existence of the smaller pattern.
Following the logic described previously, the multiplication related posts chain together like this. Think of it as a mirror, we stopped at 48 last year and now we're picking up at 84: If we follow last year's logic, we would pick up the 3 from March and use it as the date next time around.
24 x 8 | 8 x 12 < > 28 x 3 | ? x ?
Much of the chatter from Twitter is omitted, but it seems that it has a potentially identical end goal, even if some of the same numbers are utilized in a different way. Note that only a single entry per "pair" makes it over to their Facebook account. This is what we know so far.
2016 - sum = 48
6 + 6 = 12
24 + 8 = 32
14 - 10 = 4
? ? ? = ?
? ? ? = ?
? ? ? = ?
Their approach to their YouTube playlist structure has been thoughtful and at times playful. Try subtracting the numbers of some of the entries from the overall number (145) to se what type of "companion" you end up with (for example, 72 and 73 are "SATellite ANthem ICarus" and "XYZ", interesting after they spelled out L-M-N-O-P with their first few social media posts) You can also add some of the duplicate song values together to see where you end up. They might ask you to do something like "Split Your Infinities" when you find a third instance in the list of the first 2 songs that you added together, for example.
Example of a playlist easter egg:
In the end, it's impressive to witness the care that went into assembling these playlists as a companion to what they have been establishing at their Twitter and Facebook accounts. It provides information that leads one to speculate on future posts. The only drawback to the playlist assembly is that due to the number of repeats, and the proximity of some of those repeats to each other, it detracts a bit from being able to appreciate the playlists at face value. The playlist construction definitely prioritizes the subliminal/easter egg aspects over providing a good flow for the everyday casual listener.