M
Yamato mentions when Luffy is attacking her, that he reminds her of Ace, indicating Ace and Yamato fought. Perhaps Ace wasn't there for extremely long, but long enough to hear about Kozuki Oden (with a mask) but not personal enough for Yamato to reveal herself to Ace.
Who knows, Oda has to explain it in a flashback anyway soon
Who knows, Oda has to explain it in a flashback anyway soon
I really doubt that this WB inaction plot-hole can ever be closed.