With Colt, most of the time the serial number was written on the outside bottom of the box, particularly with pre-WWII guns. Post-war, some boxes were used that came with plain cardboard sleeves (National Match pistols in "trophy" boxes and dual cylinder Frontier Scouts are two), and the numbers were written on the sleeves. When the styrofoam boxes came into use (around 1974), serial numbers were usually written on the labels on one end flap of the cardboard shell. Even later, they were computer printed on the labels.
I have seen many pre-1974 Colt gun boxes with various numbers written or stamped on the labels. These numbers are almost always different from the serial numbers. I believe that these non-matching numbers were inventory control numbers applied by gun sellers.
- - - Buckspen