Back in my 1e days, when errata was, at best, hard to find, I didn't write anything in my game books. Not because they were sacrosanct; just because I knew the game so well I didn't need to. In the 3e era, or rather, the era of the internet where errata is posted almost immediately, I have taken to writing in errata or taping particularly long bits of errata directly into the book where they belong. I just don't see gamebooks as being keepsakes or heirlooms; they're to be used.