"UD320F-40-B1"

What does the "UD" and "B1" stand for?

This is a CPO gun if that matters.

Thanks

All CPO SIGs have the "UD" label. That's their code for CPO.

As for the rest:

320 - Model P320
F - Full size
40 - Caliber
B - Black
1 - Excellent

Additionally, when you see UDE, the "E" denoted full capacity. Without it, it means capacity restriction. Is yours 10-rd restricted?
For the P225, P239 and others with the normal less than 10-rd capacity, there is no UDE, and it will always be UD.

Thank you, sir.

U da man

edit: And it has the 14rd mags so maybe the retailer switched them out