And MR, that is somewhat true. Although I’d imagine that if the ship was considered a prototype in TLJ that they would have made at least one more since then in the year gap between films.
Well, the TIE Silencer from TLJ is not the same model as the TIE Whisper in TROS, so one could pretend Kylo asked for a newer set of prototype fighters once he became Supreme Leader (and ship progression in-between Star Wars movies is nothing new, so…)