> Sometimes they did not work despite being to all appearances character for character the same as the book, and I was often left with no idea why.

The book may have been wrong - between 2000 and 2005 there were a ton of programming books that were flat out wrong. Many of these were C books.

Just one example: the examples from https://wozniak.ca/blog/2018/06/25/1/index.html are full of UB and are almost guaranteed to crash.