My take on C before D:

The phrase first happened in post https://qmap.pub/read/3328 dated 27 Apr 2019 as "C comes before D". This post alludes that C means Comey and D means DECLAS.

The last post of Q https://qmap.pub/read/3570 dated 1 Aug 2019 mentions "[C] before [D]". I take it as a clarification of the first post, because he says later "[C]oats before [D]ECLAS".

Q references two twitter posts about Coats:
1. Schiff positively about Coats: https://mobile.twitter.com/RepAdamSchiff/status/1098261545551884290
2. Brennan positively about Coats: https://twitter.com/JohnBrennan/status/1155797879300210688

Actually, this has been solved by an anon @ReIncarnatedET on Twitter even before Q acknowledged this.
https://archive.ph/zCtbj/image

Q quoted this post with this comment
> Speed accelerated +5
> Q

https://qmap.pub/players/read/116 https://en.wikipedia.org/wiki/Director_of_National_Intelligence
also note: https://en.wikipedia.org/wiki/Talk:Director_of_National_Intelligence (there was a snippet about Ratcliffe in this article but it's removed now and there's a talk about removal)
> The director produces the President's Daily Brief (PDB), a top-secret document including intelligence from all the various agencies, given each morning to the president of the United States.[1] The PDB is seen by the president and those approved by the President. Other than this the Director has no authority to issue orders or to instruct anyone to do anything
Ok
> Further, by Presidential Policy Directive 19 signed by Barack Obama in October 2012, the DNI was given overall responsibility for Intelligence Community whistleblowing and source protection. 
Whistleblowing? Haven't we recently seen a lot of "whistleblowers"?

Therefore I think "[C]oats before [D]ECLAS" is the best solution of the "C before D". Maybe there are more hidden solutions and anons may think that there are, because "3328" was the last Q post, but there's a deeper connection between this drop and the previous drops.