I think due to their stack they may at times interact differently so some are after long while, quite surprised (but also Es, Is or less frequent psychological stuff) when they find out MBTI or functions exists or that theres even 1 single person that function in a similar way, so some may feel relieved or very surprised or some sort or acceptance or validation(neutral sort of way) during the time they found out. But all types do a well.

But some may blend in more or private in some ways or for different reasons, some they can some they cant. So they themselves or others may not tell if someone was an infj or (maybe neither people knew such a thing existed), but some can or show it more but subtle way or form (general convos, interactions, styles etc).

In any case why do they make such a big deal about being rarest? Seems like a bad thing to me.

I don't think most do it on purpose or at another's cost, though I see what or why other think of the fuss, like they are doing stuff or battles and others are not in crowds, but half are maybe, over all spread, just ratios. But they, just maybe result of functions or adolescents development think things in many perceptions or to make it all work, fit or make sense of. Then theres also their other function stack but true for all types also sensors, intuits, etc. Or just giving themselves some encouragement but if their young it sometimes can be at another's expense from forums (own forums or others forums or as a whole). Or also the whole similar/familiar though process thing, they may just try to communicate via certain posts, but alot it may apply for any types, some some may be more personal or relates to it so its posted. Or it could be due to the private or misunderstand of their types, and others or that some social media capitalise's on and that may be unfortunate for both themselves and other types.