Best answer by BillF
After some experimentation, I am pretty sure that the "scheduled" index is different from ones initiated on command. I added a new album, did an index, and verified it was incomplete. I repeated the index several times -- all produced incomplete results. I then changed the schedule to index a few minutes in the future and went back to doing other things. (Sonos was playing music throughout all of this.) After a half hour or so, checked notifications and was told indexing had happened. Checked library, and index seems to be complete.