Not sure.  The T means that it is for Windows 32 (think nT).  The C
means it is in the first series of fix packs (TC1 is the first GA
release - TA1 and TB1 are never used, not even internally).  TC2 is
the first fix pack; TC3 is the next.  Sometimes, a version goes to TDn
(so, 7.31.TD8).  AFAIK, the highest I've ever seen the letters go is
UE1, which was used wit 6.00.UE1 - and was actually the first release
for GA.  There was a UC1 created, but pulled in final pre-release QA;
ditto for UD1 (which was embarassing, internally, a decade or so ago).