So, what does THAT mean, exactly. Could it be, somehow, that someone like me who is on a Y ticket using a GUC to get into D1, or possibly a D1 award ticket won't get a so-called "invitation"?

I'd be peeved if I was in true D1 using a GUC or miles and denied entry.

As to dress, I remember YEARS ago, back when CO was partners with NW, I was flying LIM/EWR very early AM. I was in the airport early, even before the check-in counter opened. I was first in line for F/J check-in. Just before opening the counter, the agent, without speaking to me, literally picked up my bags and dragged them to the back of the Y line. Confused, I asked her why she did that. She said that, that line was for F/J. I told her I was Platinum Elite (the highest level at that time). She apologized, an allowed me back into the J line!