Currently it is not possible to invoke a re-indexing of facial recognition data at either the global or folder/collection level. For my purposes re-indexing at the folder and collection level would be sufficient.
Reason: when a face is removed from a previously indexed image it is not possible to automatically recognize faces other than reviewing many images and manually applying a face region.
Yes, it's not "suggesting" matches for vast swaths of my database. So if I have a group of five people, one of whom I know. The other four will just sit there. If I meet them a year later, I have to explicitly search past photos for them. It doesn't go back and suggest "backwards" as it were.
I don't want to re-index by drawing the boxes better. I want to re-index by getting suggestions for people added to the database before the keyword was linked to a picture. About 1/3rd of my currently "unnamed" people have no suggestion for who they may be and there are pictures that are near exact duplicates taken seconds apart that it doesn't even "suggest" the person keyword, let alone match and group them into a stack.
"I don't want to re-index by drawing the boxes better."
The Find Faces Again command re-runs the face recognition (suggested names), not just redrawing the face rectangles.
"About 1/3rd of my currently 'unnamed' people have no suggestion for who they may be and there are pictures that are near exact duplicates taken seconds apart that it doesn't even 'suggest' the person keyword, let alone match and group them into a stack."
If face recognition is not working well for you, it would be best to start a new topic (a bug report), since this topic is about re-running face recognition, and that feature is implemented.
I took photos of a group with 10 people in it, two of whom look somewhat similar. A colleague helps five of the people including the two similar ones. If I were to run "re-index" on this image and it redraws and makes new suggestions for all ten people. How would I distinguish which one was which?
Additionally, I shouldn't have to relabel 27,000 faces to get new suggestions on the remaining 7,000.
To me this re-index feature is somewhat useless and does not address the problems that I've seen occurring or those that others are describing.
"I shouldn't have to relabel 27,000 faces to get new suggestions on the remaining 7,000."
Agreed. That you have 7000 faces that LR isn't identifying is a serious issue that should be in a separate topic.
But this feature request (and the thread in the user forum that motivated it) was about very specific, narrow functionality: Re-running the the face indexing/matching on a photo after you've deleted face rectangles from it. Originally, that wasn't possible. Now, with the Find Faces Again command, it is.
The Find Faces Again command also helps some users upgrade to the new algorithm introduced in 7.3: "If you've previously run face-detection manually on your photos, perform the steps recommended below to upgrade the existing face records in your catalog to the new face engine. ... The steps listed below are not required if you have enabled the Automatically Detect All Faces In All Photos option in Catalog Settings."
But Find Faces Again just reruns the existing algorithm. If the algorithm didn't find matching faces the first time around, rerunning it won't make it any better the second time.
Adobe tends to prioritize and respond to the topics that get the most replies and votes.
But neither of these posts directly mentions what seems to be the most serious concern, that you have thousands of photos that aren't getting good suggestions. That deserves a separate topic directly describing those symptoms.