Oh my word.
I think what amycat is saying that is that when Suzanne Rushee's mom sends in a rec/legacy form for precious little Suzanne, she is not going to write "Suzanne is a legacy but she is adopted." She's just going to say "Suzanne is my daughter and she is a legacy and I will just die if she isn't an Alpha Beta Fish like me!"
Now, the Clownfish chapter of Alpha Beta Fish is going to get this rec, and say "Hey, cool, Suzanne Rushee is a legacy." They aren't going to say "Mrs. Rushee says Suzanne is a legacy. We better call and make sure she's her 'real' daughter and isn't adopted or a stepdaughter or anything fishy like that." The point amycat412 was trying to make is that nobody could know she was adopted unless she said so! It's not like they see pictures of her mom and say "Oh, they look nothing alike, she's adopted so she isn't a real legacy so we aren't taking her."