when did bn actually start removing the C&S lettering from the units i model early 1980 would i be okay having some 3 digit C&S units mixed in with my standard power i have seen some pics in mid late 79 that have the # digit C&S but i can'tfind any after that thanks for any help you might offer
Short answer: Yes, it would be ok. Obviously how far you go with it depends on how strict you want to be and how much work you want to put into finding out. There are at least a few on Charles Biel's site with C&S sublettering during the early 80's. I seem to recall that at least a few GP38-2's had sublettering...for sure FW&D I'd have to check on C&S.
C&S was gone on December 31, 1981 when their line Denver-Wendover was absorbed into BN RR, and line from Denver to Texline absorbed into the Fort Worth & Denver RY. That being stated, I recall seeing C&S sub-lettered units at least well into the 1980s. Lettering/numbering in some instances was likely not changed until units were shopped. Boxcab E50
We had some C&S bleeding through a few engines still running around out there.But I do recall seeing one go through my home town in the late 80's.