There is an issue with disassembling,
It is impossible with any set of pincers, to disassemble decorated leather fragments.
It's reported that the same issue exists for Corduroy fabric.
If anyone has a solution to this, it would be greatly appreciated. It's currently impossible to level LW or Tailor past 40 because of this issue
edit: I found a solution to get passed this problem, have a higher level leatherworker disassemble Shagreen, you can then retroform those parts for use.. not ideal, but it got me through 38-48

(the same solution should apply to tailors with the same issue)