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