Well, we now have the benefit of hindsight. Before these girls were found, it was theorized many times Ashley Summers was related, and so far that hasn't panned out, yet Michelle Knight was found with these girls, and up until she walked out of that house, there was never any connection made between her disappearance and Amanda and Gina being missing.
I bet if it was really investigated, there would be others with the same level of 'connections' to Amanda and Gina as AC had.
How many people had a daughter that was a last known person to have seen Gina?