So the past weekend I watched the videos by GM Eugene Perelstheyn

The King's Indian Defense 6...Na6 Variation

I found it very interesting and decided to start play Nf6 against d4 again. So I was with my parents this weekend and I went through my dad's old chess books. And I found one on the king's Indian. It's written by M.Eeuwe/A.Becker copyright 1978, and it's based on an earlier 1973 German book.

The book is from a series called 'chess theory' and it covers King's Indian, Grunfeld, King's indian Knights game and Old-indian

The only Knight a6 I can find there is in the mainline on the seventh move AFTER d5

Can someone perhaps shed some light on this? Was this line not popular back then. Or considered inferior or just hardly looked at. Or simply forgotten in this book??

I just noticed that this book is part 2 of 2 of half closed games but since the mainline king's indian is in it I don't think that matters

Yes I was afraid of that, it's a pity because it's a good book, I'll now have to read it knowing that's it's incomplete