More on thumb guides / thumb notches / index notches on the side of books

They seem to be more often called "thumb notches" or "index notches" than "thumb guides" - I couldn't find any other references to the latter other than the original XSL-FO article I had been reading.

This page has a photo of a person cutting out the notches by hand:

https://english.stackexchange.com/questions/394251/name-of-the-cut-outs-in-the-side-of-a-printed-dictionary-at-each-letter

This page has more details, along with a video of notches being manually cut with a tool:
https://printinghistory.org/about-thumb-indexes/

I thought they used machines for cutting all the notches at once! But I guess it would be hard to get the notches cut out to the exact right pages with a machine, after the book was bound. Or even if a machine was used, a person would still have to mark all the right dividing pages for the machine to cut to. For books like my big red dictionary*, which wasn't overly expensive, I wonder if they cut out the notches on each individual page, before the binding. That way they'd only need to set a specific size and position of the cut for each page, and the cutting could be done automatically by a machine as each page was printed.

*I'm not at home right now, and can't even be certain that my dictionary does have the notches like I was thinking it did.

Found some videos:

This machine requires someone to find the right pages to cut:
MSDIXER Duo, semi automatic index cutting machine:
https://www.youtube.com/watch?v=xoiYQTYF6Gk

Ah well! If the machine can count pages, then it can be fully automatic:
IND-X45 fully automatic index cutting machine:
https://www.youtube.com/watch?v=eKMfz6hPdOE