A good reference is http://www.biggerhammer.net/ for configurations, serial numbers, and etc.
On all colt bolts their should be a "C" stamped on the left side of the bolt.
All Colt 9mm had A2 lowers with A1 uppers with the serial number starting with TA or NL.
If the gun was shot a lot and/or handled a lot the upper and lower may be loose. Just use a Accuwedge and that will fix the problem. I put a Accuwedge in every AR I purchased, new or used.