I've read the silver age and know Kathy and Betty started out as aunt and niece. I'll admit to be hazy on their official status between the mid-60s and late-70s (whether they officially existed, but weren't talked about or whether they'd been erased, as the golden age heroes were for a bit before earth two showed up).
COIE comes along and Kathy doesn't exist (as far as I know) and Bette has a new origin, codename, and actual name.
Then Kate Kane is created, and I've read that story. At this point she is not related to Bruce. But I don't recall any indication that she is related to Bette, either.
Then Kate gets retconned as Bruce's cousin. I've read about the story, but never read the story - so, is Bette established as being related to Kate (and thus Bruce) at that time, or did it happen at some other time? If so, when?