Maybe some other jellies can pitch in here with more knowledge, but I believe people rarely know whether or not they can have children until they’ve tried and then eventually get tested to see what is keeping them from having children.
Even then I think it’s less likely to be absolute and general thinking says “there’s always a chance”. From talking to people, doctors rarely give you concrete answers, because they just don’t know.
It’s also extremely personal, with more far reaching implications than just the ability to have children.
I guess, in short, I’m just trying to say it may not be as clear cut as “he knew”. From the combined experience of myself and the few people I’m close enough to discuss the “fun” of having kids with, one of the most frustrating things is the lack of answers.
It basically comes down to a series of “try this and see what happens” followed by tests and another set of things to try after that. It’s usually only after years of trying that doctors recommend even starting tests.