Igor went before the promotion board that consisted of Hawkeye, Hunnicut, and Winchester. But he blew the questions, IIRC, and it was implied that he didn’t make it.
But there may have been another instance of him being promoted. I count him as a minor character.
But yes, you got the third character that appeared from beginning to end.
Chaplains are a minimum of Capt once they complete Officer Basic Course; so he would’ve been promoted to Major.
Someone obviously hasn’t watch the show in a while. He was a first lieutenant for most of the show and in one of the later seasons he finally made captain after being passed over many times and watching guys far junior to him make CPT way faster.
I don’t know if that part was historically inaccurate, or if the rules were different in the 1950s than today. But he was definitely 1LT for most of the series and eventually CPT.