Yeah, I remember that point. There's an attempt to address it in that blue book, "All scriptures". Well, when I say "attempt", it was something like "yes, we know it's a long time, but it would appear that Jehova miraculously made those ancestors have offspring at a very late age, like in the case of Abraham".. something like that.
I love those phrases the WT uses when they're going to make up some lame interpretation: "It would appear that..."