The lawyers contacted the ____ involved.
This might be more of a personal (hah get it) thing, but I would be happy if "persons" disappeared from the language completely. I think other cases of multiple words are acceptable, but this one just seems silly to me. I dunno.
Legal language uses 'persons'
True, it a legal for now. It's one of those things they haven't gotten around to fixing. Or, may not fix AIN"T is like 20 years old and is still a word.
Ain't is probably at least 200 years old, and still (if we are to believe our English teachers) NOT a word. 'Persons', on the other hand, does not need fixing.
I've learning British English, so never seen "persons".
"Persons" is used in legal English in Britain.
I learnt British English; we still use 'persons' in everyday speech.
If it ain't broke, don't fix it! (Poetic license)