Dullknife, you are not that old, but correct, usually the spare cylinders are numbered to the gun, so as to "match", and thus know what cylinder,goes with what gun,,,,but once being fitted, "like" cylinders of the SAME vintage gun may simply just drop in ( fit) into another gun....so when onewants to locate ,find another cylinder for a gun they have and may be >missing" the "spare", once you find one that "fits, works ( times) properly, easy enough to remove or add the proper last 3 digits of the "new" guns serial numbers, and thus, "match 'em up again...."
I had a cylinder for the OP< but by the time we heard from him, we had sold it the next gun show,,,cannot keep them them long enough..... 8) :roll: :wink: