... what about books like "Die Kunst der Verteidigung" by Kmoch (The Art of Defence), where you are not sure if the lines where checked with an engine or not? ...
If I remember correctly, Kmoch died in the 1970s when engine availability was limited. It is not likely that a subsequent revision would have been done without telling the reader.
There is a lot you can say about chess books. But one thing I really cannot understand: chess books with diagrams without information who has to move. I belong to this category of people who know that you should not only read chess books but work actively with them, this means, I should take a diagram, set up the position on a physical board, analyse it, write down my ideas (without moving the figures) and only after doing so I should compare my ideas with the author's analysis. But in a book without information on who is to move I have first to check this out, and this means I will see the first move. This is weird!
One of this books is "Angriff und Verteidigung" by Dworetski and Jussupow (Attack and Defence). I had the opportunity to ask Jussupov why he did not give this information, and he was completely surprise with my question - he did not know this. I mean, in a position where one side is given check I can easily conclude who will play next, but what about the other positions?
Another problem with books is that old books being reprinted are not always updated. This is amazing! There is another book by Dworetski where the author tell you how to build up a repertoire using a card box, this mean, without a single word about the use of computers in today's chess. Would it be so difficult to give at least a footnote in this chapter with the information where to get more actualised stuff on this? Probably not. Or what about books like "Die Kunst der Verteidigung" by Kmoch (The Art of Defence), where you are not sure if the lines where checked with an engine or not? Do they really think you should do this job yourself?
I know that publishers have to save money, but there are some limits to what they are allowed to do.