Quoted:
Someone probably knows this stuff off the top of their head, but I did some comparing a while back.  The info gathered showed the SP1's seem to follow the same time line as the military uppers, just years later.  Comparing the SP1 data base to the chronology of the uppers variation thread it appears you got it.

Here is what I came up from the two threads in the retro forum:

SP1's - No forge to 77, a brief use of CK (early 77?), then mainly CM with some CH's in the latest years.

It appears the CK uppers were only used on regular military M-16's from 72-73, brief in comparison to others which is consistent with their brief use several years later on SP1's.

On a side note, but related, you posted a picture of a SP1 upper with a F/A in another thread - I'm guessing it's a CH. I have a non SP-1 CH, no proofs with F/A, no bump.  I'm thinking that the small use of CH uppers in the later years of the SP1 line are the reason we see some limited SP1's with F/A's.  The rifles in the SP1 data base with CH uppers don't mention a F/A either way so it's hard to confirm.