I did ask for advice from fellow trans and genderqueer and non-binary people
elsewhere in this forum. In case anybody reads this and wants to give advice, support, or empathy.
Possibly. It's also in principle possible that your dad doesn't want to own up to having known about it. I don't know him, so I can't say if that's the sort of thing he'd do.
I did consider that possibility. That
is the sort of thing he would do, but knowing my mom and knowing my dad, especially who they each were back then (sadly my mom did not grow and change), I do think it's more likely that she never told him. When I asked each of them, she said she didn't know if he knew, and I can't imagine how she'd not know that if they talked about it.
I do think when I asked him about it, he'd have been more likely to admit he knew but excuse his inaction because people didn't know back then. And he and I have had conversations about queer people he knew when I was a kid and he did say he hadn't heart of the word transgender (or even the word bisexual when I came out to him as "into everyone" back in the early 2000s) . I dunno. Part of me also just wants to have faith in him.