My mom was trans. When we talk about the past, we used rather mixed pronouns. When I met my older sister for the first time, we sat down and had a long talk about "Daddy" and she made sure she wasn't offending me before using male pronouns, simply because she grew up with "him" and I only know "her". My biomom does the same thing, uses the correct pronouns for present/future tense and the old pronouns for talking about "way back when".
I don't think there's anything wrong with this, but only because I mentioned it to my mom and she said it didn't really bother her. To her, pronouns are less important than family we see rarely, once a year if we're lucky.
In your case, hizmom, you're probably right about making the proper pronouns habit, simply because people are still getting used to calling your kid "he". Once it does become habitual, you could probably be a little more lenient when telling stories about the past.