MisterX & BigG,
Sorry to be so long in getting back to you both; I was called out of town unexpectedly and am only now catching up with hobby-related matters.
MisterX:
My sources of SN dates only go to 1985. I'm surprised that Colt would reuse the same prefix letters both with and without a letter suffix, but if that's what yours is I can't argue with it! As has been noted, an "E" suffix typically indicates a gun from the "Enhanced" Series '80 run. I don't know, with accuracy, the date span of the Enhanced guns, but mine was bought new in '94.
BigG
I'm going to have to disappoint you, too. I have never seen a Colt O-frame with a letter in the middle of the SN.
Steve