In SE11 if you double-click on the data element (FMCCRDUNS) you can see that it belongs to the package FMFG_CCR_E (Interface to Central Contractor Registry (CCR)), so I'm guessing it's not meant to be filled in in the SAP transactions but is part of some kind of, well, interface and possibly an add-on of sorts.
You could probably expose them as custom fields, but it might not be a good idea.