Is there some way to force facial recognition to run again?

FR works fine in some cases, seems asleep in others. Usually this happens between folders (pix in some folders have FR, pix from some other folders do not), but sometimes *within folders (some pix have FR, some do not). I am speaking here of photos of similar clarity. I would not expect it to recognize some of the fuzzier photos I have.

Second question, in backing up my catalogue, as a precaution, I have backups done at different times (1, 2, 3, 4). I thought if one went bad at least I would have an alternative. Reading some of the discussion around FR, this might not have been wise? If so, how would I fix this?