On the other hand, when the Sao Paulo was renamed as the new Defiant, it had the perhaps even more special honor of retaining the NX-74205 registry of her predecessor without any letters...
DS9's producers wanted the Sao Paulo's registry to be NCC-74205-A when it was renamed Defiant, but since most of the time we saw it it was stock footage from previous episodes, it ended up keeping the NX-74205 registry.