One of the many things that are wrong with text books is that, with short funds, some are used much longer than they should be. If that isn't the case the "new" editions often just copy older ones.
When I was in grade 7 out socials text had a chapter on dinosaurs and "cave" men. The dinos were said to have died out 5 million years ago. I, as usual, loved finding errors and eventually got my teacher (not easy) to admit that it was wrong. The figures at the time were from 60 to 70 million years. While this was a looong time ago that I was that young it wasn't so long to give a differnt answer.
I think, but no longer remember for sure that the text at the time was originally written pre WWII. It was still in use 25 years later.
The age of the text or the material is it built from is important when considering it as a source.
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