The most cinderellas I've seen at once in the last few years was an album of 1200 Swiss exposition stamps at Noble Spirit - which I was happy to get for $600. That's about the only way to buy these for under $1. Old Louis has had some other multi day cinderella auctions in the past - usually Russian material - some of them may have added up to about 1000 stamps.
So 40,000 over 4 days - I wouldn't be surprised if their claim that it was the largest sale in the last 100 years was true.
Philatelic exhibition stamps is a whole subspecialty in itself. A man named Drummond has put out a huge catalog of them:https://www.ebay.com/itm/3526623952...mkgroutmp=no