IMO the biggest change over the last 20+ years is going to be in the health and safety of the techniques. By way of example, I read a lot of books on jewellery techniques, the older ones all advise annealing by dropping the hot piece in a bucket of powdered asbestos. There is still likely to be a lot of good information, and the basic materials may not have really changed, but some of the methods of working with them have, so think critically about what they are suggesting you do.