I have a 2019 Uberti pocket navy with a box "CU", 2 Old Silver Dances with box "CU" ,an 2018 1851 RM Conversion with a box "CT" then the Pietta with a box "CZ" Last month I picked up a Uberti 2nd Dragoon with a boxed "21".
Another observation: sometime in the past few years Pietta has started putting dates on the underside of the barrels. These 4 number dates do not appear to always coincide with the proofing date. My 2 Dance "CU" revolvers have "2019" beneath the barrel, yet my "CZ" 1851 has a barrel date of "2018"! I suspect these are the production years of the barrels themselves, with the proof date reflecting final assembly and proof.