Re: USS Copernicus, NCC-640 or 623?
It might seem less ludicrous if we assume that newer build Oberths might incorporate upgrades and so forth, and be essentially "new" ships in an older hull. I can see where constantly reusing the same models gives the impression of cheapness to the fans, but on the flip side I can also see where futuristic technology might extend the life span of a unit far more than is the case now. The Battletech universe seems to do this frequently, with many designs having seen up to a century or more of service, albeit not in a single model usually.
"My dream is to eat candy and poop emeralds. I'm halfway successful."
Catbert, Evil Director of Human Resources