Dupe with superhard diggin skill cannot dig "hard" things

Your dupe is missing level 1 digging, so he can't dig level 1 material like fossil, he has level 2 digging so he can dig level 2 materials. seems not logical but it is

If you mouse over the skills in the skill tree  it states witch materials to dig it unlocks.

Edited May 22, 2021 by Upload

I would expect level 2 to have level 1 + XXX

Adding to this the Decorating skill

The masterworks bonus skill is actually pretty nice because you can skip the middle skill without really loosing out on anything. Not only do you get the free morale from masterworks, you kinda also get the middle skill for free too because the only thing the +2 to creativity does is make them sculpt or paint faster, and its such an uncommon errand that making it go just a little faster won't matter.

 

However, if you ever respec a dupe with a bonus masterworks skill, you unfortunately loose that free middle skill because you have to re-select all of your skills again, including the free ones. The free ones just don't cause any increase in morale need, but you still have to select them and need their pre-requisites first.