No point in worrying about it because it is Colts 1991 which came out in 1991 which if I recall correctly was a no frill basic gun with a lower retail price than the normal production runs at the time .
Nothing special about it at all no collector value etc. because they are still being produced in good numbers .
If it were to have any added value for any reason it would be greatly reduced because of the scratches made by someone installing the slide stop commonly referred to by 1911 lovers as "Idiot scratches" .
Did you call Colt and ask them when it was produced? All you have to do is give them the serial number.
You might want to take the time to change the title, since there is no such thing as a 1991 A1.
I was just teasing---- I had typed up basically what you see below--- but I highlighted something to check for spelling the whole thing deleted-- frustrated I hit post.
It is a Colt 1991A1 but the the only real difference between what you have and an original 1911 is that it has a model 80 safety (ie a firing pin block safety which many manufactures (Kimber, S&W, ect) have now anyways hence the joke-- you don't have a 1991 you have a new 1911-- bad joke sorry ). It is the economy version of Colt's 1911-- they sold for about $500 (while at the time Colt's 1911's sold for 700-1K). The early versions of the 1991 also had plastic triggers and rubber grips. Does your Colt have a plastic trigger? If so you probably have a early model.
Anyways I guess I should have rephrase my statement- you have a Colt 1991A1-- but it is a 1911. I saw one sell (never fired-- clean as a whistle) for $700.