Note that apps built from the SDK don't have access to the full history, only up to some cutoff. I tried a couple over the years and wrongly concluded Spotify deleted your history after some time.
The data download does contain everything, which was a very pleasant surprise. I didn't think I'd ever see the data from the couple years gap in my last.fm.
There's probably one person nursing some horrific bogslop software that frequently breaks but absolutely cannot be rewritten or changed (because it was someone's pet project) and frequently has to be manually twizzled to get things out of what is probably a hostile data retrieval environment and they're just TIRED and that's why there's a 30 day leeway because otherwise the Data Retrieval Goblin would be way over the line of overwhelmed rather than just under it all the time.
Probably.
(I realise I've likely described a significant percentage of companies there.)