The loading gate number is an assembly number that should match the number on the bottom of the frame under the trigger guard. All 1st and ar least most 2nd gens should have it. Not on any 3rds that I know of

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Gates were not interchangeable, and had to be hand-fitted. In order to make sure that after finishing (bluing/case/plating) the gate and frame came back together, either an assembly number or partial serial number was added. If an assembly number was assigned, then it will also be found somewhere on the frame.

Not all Colt models used the same gate numbering system. Some models shifted their gate numbering system all through production. A good example of the latter is the Colt M1878 DA, which sometimes used an assembly number, and at other times used a partial serial number.

If a gate has no number, then I would suspect a replaced gate. Those case hardened gates sometimes broke off where the shaft section meets with the external gate. I have seen several examples of this brittle failure.

 

I have 3 third gens with partial serial numbers, they are all Custom Shop

 

I’ve had three third gen guns and they all have had the last three digits on them. Pete