What if you activate the option "update all configuration for your folder card for the variable Project number?
Hello Salvador I don't believe this is possible in EPDM (at least not without API)
The ability to link a variable's value on a file card to be inherit from the parent folder card is intended to be a static method. It only works the first time you add a file into the folder in the vault. If you then move the file somewhere else in the vault, the value will not update to the new folder.
Linking to a value in Excel or Autocad is much more dynamic as you change and update the file.
I hope this helps answer your question.