Something like that might also explain why NCC-602 and (possibly) NCC-623 aren't Monoceros or Cygnus class vessels.
Alas, ST:TMP tells us that the Cygnus class wasn't "approved but infinitely delayed" - at least one of the bird-named ships was completed by the early or mid-2270s, as USS Columbia is mentioned, her FJ registry explicit. But there are no onscreen references to the Monoceros class or its individual ships, so perhaps that class was never built and early Oberths were constructed instead in this registry range? (This would also remove the annoyance of USS Aries which appears to be contemporary to the very different scoutship of the same name from TAS "Eye of the Beholder"...)
The vessel from "Eye of the Beholder" was Ariel
. Close but different banana.
Interesting theory though.