I am happy that Vault 2016 restricts this scenario below with overlay XREFs. However this means that data checked in with Vault 2014 cannot be checked back in after a few small changes. This is a huge confusion to the users because they don't see the broken link in the XREF manager.
In the scenario below, the user must open every Overlay XREF to find the unresolved XREF. This can take hours when I have 10-100 XREFs.

Vault Solution: Provide the path and filename of the DWG with the unresolved link. Bonus points for prompting to open the DWG with the unresolved link.
AutoCAD Solution: Provide a view mode to see all file relationships by ignoring Overlay (don't change what is displayed graphically).