brookline, I wish all TV shows and movies did as much research on Greek life as you do

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What's been said is correct. Signing a bid card is, in effect, signing a bid. I think what you were thinking is if you put only ABC and DEF on your bid card, and XYZ offered you a bid out of nowhere. You have no obligation to XYZ, but you do to ABC or DEF if one of them offered you a bid.