It is clear that there is a separate "plate" or captured threaded nut or "something like that" behind each hole for each of the three bolts individually on each hinge mount area. That surprises me; I expected to find a single plate with three holes tapped in it..as you alluded to.
On the problem side, two of them are sufficiently captured that the bolts thread in by hand just fine. The remaining one, however, freely "spins" when I try to start the bolt.
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