This surprises me. I interpret “Dardanelles closed” as the black sea, and that the small part before the Bosporus is fair game (i.e.: boarding from Bulgaria/Romania). Therefore, I have made that move (and allowed that move) in various other games as well (including in the previous round).
I think my confusion herein arises from the fact that the prerequisites specifically say “Dardanelles closed”, and not “Sea zone 16 closed”, which would avoid all confusion.
You are the first to point out to me that that move is illegal. I think you know the rules better then me, so hereby the revised version.