What is the etiquette or protocol when you happen to know someone’s name, but their posts always reference the forum user name? Is it bad etiquette for someone to refer to me as David for instance, instead of @cogmission ? Does it matter to anyone?
I don’t think it matters, but if you want someone to be notified by Discourse, you should use their @forum name. The notification settings are adjustable, so some people will get emails when they are mentioned.
My thinking is that for whatever reason, someone might prefer a certain level of anonymity - and that maybe it should be assumed true for participants by default?
For the longest time, I struggled with whether I should refer to Matt by his real name in arenas where the only title exposed is his moniker of @rhyolight… A silly thing maybe to be concerned with - but my thinking was that he has sooooo much required of him to keep up with, monitor, answer questions, administrate the forum etc. ad nauseum - that I thought maybe keeping a certain level of anonymity allowed him a certain distance so that he could take a breath now and then! 
And I also thought maybe others might also want that consideration?
Anyway… if I’m over thinking this, I apologize…