I was not welcomed to FlyerTalk until I happened to post many months later during a discussion that I was never officially welcomed to FlyerTalk.
I have no idea in which thread on FlyerTalk that occurred, but that does not matter.
I can honestly say that I have never felt unwelcome to post on FlyerTalk since I first posted in December of 2002.
Regardless, I believe that one can say “Welcome to FlyerTalk” to virtually any FlyerTalk member without straying away from “etiquette”, as long as one’s “Join Date” is not later than the “Join Date” of the FlyerTalk member to whom they are welcoming. That can be a bit awkward. However, expressing and extending a welcome to a fellow FlyerTalk member is usually meant in a positive way.
So, to all of the FlyerTalk members whom I have not said so yet, welcome to FlyerTalk!