Re: 3 Registries for the Yamato?
The registry for the one in "Where Silence Has Lease" was verbally given by a main hero, and used as proof positive that this was the real McCoy.
The registry for the one in "Contagion" was seen on two viewscreens (Picard's desktop terminal and Observation Lounge viewer) and might have been corrupted by the computer virus that ultimately destroyed the ship.
Usually I will go with the wag "NCC-1701-x was a binding resolution from the Federation Council that SF was stuck with"
but nothing in that says that it had to be the only time .....
"The single biggest problem with communication is the illusion that it has taken place." - George Bernard Shaw