The documentation portal is undergoing maintenance. During this period, you can't create any new user credentials. If you do, you'll need to recreate the user credential after the maintenance period ends.
You can delete a relationship record version that is effective for a specific period. When you delete a relationship record version, the MDM Hub inserts a new record version in the cross-reference table associated with the relationship base object. The effective period of the record version is the same as the effective period of the relationship record version that you delete. Also, the MDM Hub sets the deleted indicator for the record version to -999999999, and the hub state indicator to deleted.