There's an amusing memo where Justman rags on Theiss about a mistake re a fellow ship Captain's insignia, but by the point that memo was written they'll already blown it and have different insignias for Decker and Tracy so the die was cast.
That's a story I'd like to hear or a memo I'd like to read.
Considering all the fuzz TOS made about the prestige and privilege of being a starship captain (including Commodores) I think Theiss draw the correct conclusion that starship insignias should be individual and unique.
With the merchant marine it's a different story. Rewatching "The Trouble with Tribbles" recently I noticed during the K-7 brawl one bystander wearing the Antares
costume from "Charlie X" (and another one wearing Finnegan's costume).