I sort of like the ambiguity with canon and on-screen evidence, because it reminds you two things: this was a show where the past wasn't hacked out (and I would argue that beyond good strokes, that's a good thing. Earth had wars. We went to a dark place. Met Vulcans, crawled out, had a war with Romulans, made the Federation), and it allows you to fill in the blanks with things you like instead.
I can pick from Starfleet Museum to FASA to Axanar to The Romulan War to a few novels and be content.
And besides, it's not like a technological society has a handle on history just for being technological. This forum itself could provide ten different views on the history of the US, much less the world, and a lot of key events that buffer one's sides view might be completely unknown or unheard of by another. I sort of see the Federation in that angle, if we look at the show, they barely care about anything from 2161-2250, 2293-2364, 2385-2399...
The meta reason, again, is that the writers didn't care to hash it out. They could. They could make up whatever in a month and say 'THY CANON', but honestly, that might just cause more problems, chaining every generation to the other. The only thing I would like enforced is aesthetics, but even that is flexible - the Connie in ENT trumps any prior connie, and people are fine with DIS's connie, for example.
There are still many silly things, but eh.