Just to bolster @wrp51's analysis that little bit more. There is...

Just to bolster @wrp51's analysis that little bit more. There is a gap between August 2017 and the 2016 filing which the skeptic in me thought could mean not all four of the patents were filed in December 2016 (some could have been filed March 2017 and still listed in the August 2017 announcement). However, this is not the case! Indeed a January 23rd 2017 announcement, "4DS GRANTED 17th PATENT" states at the bottom:
"Established in 2007, 4DS owns a patented IP portfolio, comprising 16 US patents granted and 7 patents pending, which has been developed in-house to create high density storage class memory. "
Obviously the 16 granted became 17 granted with that announcement, but 16+7 = 23 patents. We now have 20. Leaving 3 patents pending that were submitted before Jan 23rd 2017 (likely December 2 2016 with the 20th patent).

While there is a chance they aren't granted, given they got the last 20 granted I can't see that these final 3 won't be. And as @wrp51 has assessed, these should be granted shortly.

According to this visualization (current as of Jan 2019), the average time for a patent to be completely approved is 23.7 months.



https://www.uspto.gov/dashboards/patents/main.dashxml

However, in 2016 when the patents were submitted (as proven by the Jan 2017 4DS announcement listing them), the average wait time was 26.8 months. That means we're coming to the end of the average wait period.

Assuming that the average wait time is what 4DS will experience (obviously average is not a guarantee), then I would expect a patent announcement within the next 6 weeks.