This is not a typo, the chances does not sum to a total value, means you can still receive nothing from that.
Based on the data you provided:
- First you have 67% chance for getting Stone.
- If it fails, you have 25% chance for getting Copper.
- If it fails as well, you have 17% chance for getting Tin.
If you didn't receive Tin as well, you get nothing.
I hope you understand

I know you've mentioned it changes but pretty much everyone wants to at least know the formula for when you buy the drop rate increase so we can at least plug in our player level, upgrade level, etc.
It means that improving the stone drop is actually nerfing the rarer components drops? it seems very punishing from a user PoV. Shouldn't drop rate be computed with the rarer first ? (thats how most RPGs compute drops for example)
If it stays that way, we could use a "sell" button for upgrades. Also, could we know what's the relation between increased drop rate upgrades and the % drop rate in a cave. Is it a flat 1% per level ? A proportional 1% compared to the base drop value ? something more exotic? Its hard to decide whether an upgrade is interesting w/o that kind of information
Agreed. If you've upgraded stone to oblivion, even after they're going to reduce the upgrade limit, it still nerfs other minerals if it picks stone first.