I agree with John Taylor Gatto (A Different Kind of Teacher, 2001), that textbooks are generally not very effective:
I came to see that the school edition wasn’t a real book at all but a disguised indoctrination. The book had been rendered teacher-proof and student-proof.
However, there are cases (such as Mathematics) where a textbook is important. I homeschool our daughter, and I purchased Mathematics; A Human Endeavor, by Harold Jacobs. I have the second edition, copyrighted 1982. I have reviewed many textbooks and options for studying math, and believe this provides an outstanding overview. Since the fundamental ideas of math do not change (at least at this level), there is no need for constant updates. In some cases, the classic is the best.
In other cases, particularly when information is changing rapidly (such as the sciences and technology), recent updates are important. However, don’t get carried away with the idea that newest is best. Often the better idea is to read some of the source documentation, and also to explore alternate viewpoints.