Way back three million years ago when I taught grammar, before I'd forgotten half of what I knew, students would argue with me about odd plurals.
Now, I'm not sure of the technical name. I probably knew it, and have since forgotten. But I'm talking about compound and hyphenated nouns that aren't just made plural by adding an 's.'
Like passerby. Plural? Passersby. Seem odd? To some, yes. But it is absolutely correct.
Attorney general? Attorneys general.
Mother-in-law? Mothers-in-law. (For the poor folk plagued with more than one.)
What is bringing this up? "Scenes-of-crime officers" in an older mystery I am reading. Technically correct, but I'm really glad we now have "crime scene investigators."