I'll put this idea out there FWIW. On cupped boards that aren't thick enough to take the amount of material removal (sanding) to get them flat, OR where the floor is very antique, and you want to keep "the look", a hand-scraping technique can be used. I use a 1 1/2" paint scraper, and round off the blade so the corners don't dig in. For a real "hand scraped" effect, the entire blade should have a gently-rounded profile. Yu have to keep the blade sharp; a file is used almost continuously for this purpose. I have done two floors this way, both times on wide/random heart pine from about 1800. It turns out great, very little material is removed, and a good bit of the patina (old color) retained, which would be totally lost in a drum sanding.
I have also used a cabinet scraper to level a new installation of heart pine where the owners did not want it sanded. That is a more practiced technique, and very hard on the thumbs.