I can relate to both sides--child and parent. My dad had bladder cancer when he was in his 70s, back when the treatment was just removal of the tumor (no BCG or mitomycin yet). He had one recurrence, and of course we were all worried to pieces. As it turned out, that was all he had, and he died in his 80s (from metastisized lung cancer, unrelated to the blc, but related to smoking); he had been clear for some time of bladder cancer, and was on just annual blc check-ups at the time of his death. I had a first tumor in May 2006, lowgrade & non-invasive, removed via TURBT. At the two year mark this past June, the urologist found 2 even tinier tumors (pinhead size), which he removed. Now I'm on BCG, and have had one all-clear check-up since the initial 6 weeks of BCG.
In terms of what the urologist says he sees in your Dad, as others have said there are other possibilities besides a new tumor, including changes due to the BCG itself. I forgot if you've mentioned it, but how long was it from the time of the last BCG treatment to the current cystoscopy? Some people's bladders react more strongly, and the lining can stay abnormal-looking for awhile. And, as others have said, even if it's the start of a new tumor or other abnormal cells, it sounds as though the urologist is right on top of it. I'm afraid with bladder cancer, it's generally not a question of "if" you are going to get recurrences but "when", how many, and what type. I'm resigned, and so long as any recurrences I have are the same type and grade, there are not a lot of tumors, and the interval between recurrences is not too short, I'll be happy (and if something changes, I'll deal with that when the time comes).
Best of luck to your Dad.
Ann