I think the “for fun, not academic accuracy” framing downplays the issue a bit.
This isn’t about small discrepancies - there’s a meaningful difference between “this is your chat activity over the last year” and “this is your chat activity over the last few weeks of retained data.”
When “retention days” are configured (which they are by default), the wording no longer matches what’s being shown and can easily create a false impression. That’s less about precision and more about expectation-setting. Also, a wording like this can unintentionally suggest that deleted chat messages are still being counted or analyzed. Adding something like “based on retained chat data” would clarify this.
And finally, it’s not entirely clear where the “fun” is when the whole chat section in my rewind disappears simply because all public-channel messages have aged out.