Laz

Bob Justman wrote a lot of memos. Sometimes what he wrote was adhered to, sometimes it wasn't. Every time we see someone from another ship on TOS, they're wearing an insignia other than the delta or arrowhead. The Antares, the Constellation, the Exeter, the Defiant. These different insignias were designed, created, sewn onto the costumes, and the costumes were put on the actors. That's not an oversight. That shows clear intent, several times.

The only exception I can think of are the guys Kirk spoke to in the Starbase 11 bar in "Courtmartial", but I've always thought that they simply put available costumes on those actors that already had the delta sewn on rather than design new insignias and make new costumes for them. That episode was already stretching the budget wardrobe-wise, what with all the dress uniforms required, including Shaw's.