The previous-edition "hack" you describe applies to many textbooks but Horowitz and Hill is a bit of a special case. The current edition is the 3rd, published in 2015. The 2nd edition is from 1989, and while a lot of the material is timeless (part of why the book has become a classic), as you can imagine, a lot has changed in the world of electronics since 1989 and therefore the update to the 3rd edition was widely anticipated for many years. By all means pick up a 2nd edition if you find one cheap, but it is a book where it's probably worthwhile to prefer the current edition if you have the means.