If one learned German from a forty year old textbook the only problem related to that that you would experience in Germany would be that some people would think you were speaking rather more formally than expected. Learning it from an up to date text book isn't going to make you noticeably better at communicating with actual Germans in real life, that takes actual immersion in the language as it is really spoken.

And the German language authorities might well have added a new letter or changed the spelling of the word spagetti but that doesn't mean that every German has.

Textbooks are of very limited use in the real world.