In south and central American cichlids dorsal's tend to be longer and they are easily vented. Are goldfish on the same track? Are there any obvious visible features distinguishing genders? Are they vented the same way?
I'm really sorry to hear you had little luck with your plecos. Do you think there was a specific reason this happened?
They were close to 7 years old. Not sure BN's go much longer than that in captivity, though I am not sure.