We do EBCI occasionally for my CP holder...never have even tried to have her board with me.

I recall one time the A+ holder in line in front of me tried to have his 15 (ish) kid board with him and the kid was stopped at the gate but Dad was told by GA to save a seat. He did, in the exit row...

Last week I had A19 and there were 4 people in front of me. Seemed like one too many, but one of them was holding A16 and I never saw the other BPs. He handed the GA all four BP in one stack and kept walking quickly. Of course the hidden BPs were all in B group. Thinking back, I should have asked the GA to call them back and make a public display of their rudeness to the rest of the passengers.