I figure if it fits use it.
To the purist this might matter on a print so it can inspected and pass. Yes, there are full form inserts for metric threading. What really matters in your application is functionality of the pitch diameter and final fit. No real need to debate root and crest form to prove right or wrong. That is just being anal for no other reason!
Over/under sized minor/major diameter threads that do not need full strength are common. Full form threads are a bit vulnerable to damage in harsh environments. This also gives clearance for grime displacement reducing the risk of galling and other ham handed abuses. Typically it is one thread or the other(internal or external) and NOT both. You might even see a higbee cut or blunt start threads to help mimimize cross threading in these applications. Moreso on coarser threads though.