I came across  a 1990 mustang a while back and it came home with me, it is the perfect point and shoot pocket pistol. Since then of course i have been reading up on the different models of the mustang but have yet to find anything on the years that were cast and the years that were steel. The 1990 seems to be steel since i can't find any casting marks anywhere, but i would like to know for sure the dates of the cast/steel models.

I have searched just about every place i can think of and have called colt but so far haven't got past the busy signal, any help here would put to rest that question for me. Thanks

Check the base of the grip for cast marks.  All first generation Mustangs were cast.

https://forums.1911forum.com/

The Pocketlite LW .380acp was made from 1991-1987.

The original Mustang was made from 1986-1997. Stainless steel models were made from 1990-1997.