My comparatively old Panasonic DMC-FZ200 (released in 2012) has this in the manual for the playback mode:
(Face Rec Edit) You can delete or change the information relating to Face Recognition for the selected picture. 1 Select (Face Rec Edit) on the (Playback) menu. (P52) 2 Press 3/4 to select (REPLACE) or (DELETE) and then press (MENU/ SET). 3 Press 2/1 to select the picture and then press (MENU/SET). 4 Press 2/1 to select the person and then press (MENU/SET). 5 (When (REPLACE) is selected) Press 3/4/2/1 to
Note • When all Face Recognition information in a picture has been canceled, the picture will not be categorized using Face Recognition in (Category Selection) in (Filtering Play).
So it recognizes multiple faces (I think you can save about 10 faces that it should recognize by name) and prioritizes them when you're doing face-focussing. In addition, they are labeled during playback and images containing them can be selectively reproduced.
I did not use this feature, so I do not know how it's stored: I would suggest using some EXIF tags rather than XMP (but this should be relatively easy to convert). Since this sounds like the kind of feature that deserves a check in camera reviews, and since it was already available in 2012, I should be surprised if it is not buried in more or less useful ways in the menus of most current deals.