Even if you found zero recipes, that does not mean you wasted time. Maybe if you think in terms of results for that particular cookbook investment, but it is pretty arbitrary way to look at it. What if you tried to measure your return for investment on a single page of a cookbook? For half a dozen coobkooks? For a shelf of cookbooks?
If you continue buying and studying cookbooks, you will find some good recipes in some cookbooks and what you need to look for is the total return on the total of investment. I spent a ton of money on cookbooks but my life is much better for it and I have zero regrets even if many of these cookbooks yielded zero results.
So now back to technical books.
Some of these books will yield new knowledge and some may yield very little or even none at all. You may not know before you buy a book whether it will pay for itself, but you know if the whole business of buying books and learning from them is worth it. I chose to buy and read books even if some of them yield little results because I think I am a better person and a better developer for it. I learned a lot of useful stuff even if I completely ignore majority of everything I read and then forget majority of everything I thought valuable.