Very interesting indeed!

COSPAS/SARSAT was originally designed to fix beacon locations without encoded GPS signals -- two satellite passes were required at a minimum. With GPS location data encoded in the signal the precision and time to locate were significantly improved, proving to be a tremendous boon to rescuers.

When comparing InReach to a PLB, it might be useful to know if the Iridium satellites have the capability of triangulating locations where there is no encoded GPS signal. I suspect that the answer to that is "no."