The CA DOC 3913 that I once had, and should have kept, had a TDT prefix.

The first 457 that I owned had a TDP prefix.

For a while I had a 5904 with adjustable sights. It was in with a bunch of 5906 PD trade ins. I bought it because I wanted a 5904 to go with my 5906. The prefix was TDD, so it might have been part of that batch or just coincidence.

As I recall, I bought the 457 from the original owner, who was not a police officer. Maybe that was an over run gun.

My 3914 DAO which was definitely a police gun has the standard for that model UCT prefix.

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Can open, worms everywhere.