I generally err on the side of drop rates being classic since Nilbog knows way more about this than any of us. That being said, I'm sure some of this is guesswork based on patch notes, data mining code (which may be non-classic era code), and things like old forum posts. They do the best they can with this stuff.
The good news is that if you can find evidence online that something on P99 is incorrect they will usually make an effort to change it eventually (unless it's something that's been deliberately nerfed, e.g. certain item recharge costs etc.).
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