Early Bearcats from 1958 to 1970 and a few Super Bearcats have two serial numbers. The inside of the trigger guard was stamped with the full serial number so it could rematched back to the
frame after returned from being anodized . So the question is , do you have a matching numbered Bearcat ?
I checked all my old models and each did have the matching serial number EXCEPT on the Super Bearcat with the steel trigger guard.
The letter I spoke of here, "I did receive a letter from Ruger today saying that they couldn't help me concerning the starting serial number that was inscribed on the cylinders." concerned when they, Ruger, started inscribing the last three of the serial number on the cylinder face. I have some new models with and some without.