at least one of which assembled from the pieces of two destroyed airframes.

How difficult was it to "assign" a BuNo to such a hybrid?

In both the H-3 and H-2 instances that I am aware of this happening, one of the
two aircraft was listed as substantially damaged, the other CAT A, so the CAT A
aircraft ceased to exist (so I was told). At one time, I guess there were a
lot of half-destroyed H-2s laying around (gee, imagine that), so the Kaman guys
in the unused HSL hangar... well, honestly, I haven't a clue HOW such a mating
occurs. Under the light of a full moon, during a three weekend payday cycle,
the witches of Kaman gather cackle

We actually had to dig through paint to find the rivets that had been
entirely concealed during such repairs.

If the paint is what's holding it together, why bother? g

Call it professional curiosity.

v/r
Gordon