I went back to visit the fallen tree that was loaded with Osmoderma larvae, now halfway removed by a tree service, and found this elytron amid the debris that came out of the hollow where the Osmoderma larvae were (as well as several more larvae). It provides a substantial hint as to the identity of these larvae.

This elytron, because of its size, color, texture, contours, and relative glossiness, is almost certainly from O. emeri*cola rather than O. sca*bra. Also, most of the grubs and their pupal shells are larger than O. sca*bra's. Therefore it's likely that O. emeri*cola imagos will emerge from most or all of the pupal shells.

On a Web site that describes rearing practices for various beetles I recall reading that O. emeri*cola generally does not mature if it is broken out of its pupal shell prematurely. However, I have had O. sca*bra build new pupal shells, so it remains to be seen how many (or if any) of the evicted ones survive.