Funny some call the full size 1991 Series a 1991A1
The 'A1' suffix is inconsistent with past models. THe
full size Civilian Model has been the Goverment Model
which was pretty much a blued M1911A1 . In Colt's
description of the 1991 Full size, they say they went
back to the origiinal M1911 with Flat MSH and the long
trigger ( but modern aluminum ) - and modern touches
of raised 3 dot sights and the enlarged ejection port.
NIce looking 1991 Captains1911, I have recently picked
up a blued 1991 Series Combat Commander Yeah I like
\ the prancing horse on the slide as well.
Pedantically
Randall
That would be Colt that called them - 1991A1s, people aren't just adding it on. When the 1991 series was introduced in, surprise, 1991, the "A1" was Colt's spin to relate the gun to the old military 1911A1s, they even referenced the old guns in the advertising. They were parkerized at first then later the finish was changed to matte blue, they had polymer triggers and MSHs. The model number on the box label was 01991 but 1991A1 was rollmarked on the slide in huge numbers and letters, that is why they are called Orginal or Old Rollmark (ORM) guns. Also, the only prancing pony on the ORM guns was on the hard rubber grips they came with.
In 2000 the same model received a facelift with a better finish, some parts up grades, Colt dropped the A1, and changed the rollmarks and added a prancing pony, even though the model number, 01991, is the same. These are referred to as New Rollmark (NRM) guns, that would be what the OP has.
The original 1991A1 came in Government (5"), Commander (4.25"), and Compact (3.5") sizes and all had the 1991A1 billboard rollmarked on the slide.
These are pics of my three ORM 1991A1s, obviously the Commander and Compact have been modified but the Rollmarks are clearly visible on all three guns.