I think it's normal for most people, in general, to have a selective memory, and to tailor what they tell about and how they tell their history because it feels more genuine to who they are in the present. People are complicated and messy, and not everything they experience or feel lines up neatly or makes for a story that feels satisfying or comforting to tell in retrospect. Especially for trans people, where I think there is a social pressure or expectation or even just convention of having the since-early-childhood narrative, originally as a way of getting psychologists to believe that we weren't crazy and of reassuring ourselves that even when everyone else (including psychologists...) did think that we were crazy, that there would be something to hold on to and reassure ourselves that this isn't just a passing fancy, I think having the childhood narrative for validation is a powerful incentive or way that our community communicates and bonds.
So I get that it can feel frustrating or alienating or delegitimizing to feel like the signs that everyone else seems to talk about just weren't there. And I can definitely put together two different stories from my childhood by turning a blind eye to some things and spotlighting other things. One story has me engaging in gender non-conforming behaviour from ten years old, my clothing and my interest in my sister's toys serving as the canary in the coal mine that all was not well in the pre-pubertal gender utopia; the other marks me a normal rough-and-tumble guy who gets the bright idea of becoming a lesbian in high school because girl on girl is hot. Neither of these stories is right, and neither is wrong: they're willful reanalysis on a past that is altogether too easy to manipulate with unreliable memory and the benefit of hindsight.
Sure, there's always a part of me that wonders how I didn't put it all together sooner. But there's an equally large part of me wondering how I could have possibly come to the conclusion that I was trans when nothing in society would have led me to believe it was even possible for anyone, let alone me. Like a lot of people, it wasn't until I was exposed to the fact that trans people existed that I began to consider any of my inner thoughts as lining up with that. But I don't put too much stock into my childhood as a tool for validation, mostly because I know I could use it to tell whatever story I like, and I'd much rather tell the story of me, now, happy in the decisions I've made regardless of what my ten- or twelve- or sixteen-year-old self would have thought. Those people weren't me-as-I-am-now, and I am. So what they thought about their own identity isn't really germane.
Of course it can feel reassuring and helpful for other people to use their memories and their past as a way of validating who they are now. My own feeling, though, is that it doesn't sit too well with me personally.