Its in print its got to be true!!! ha ha ha...Yes, the book doesn't say anything about who had this endowment, and who measured. I agree with you, anyone can claim anything, advertize it, print it. Doesn't mean its true.
Somewhere I have seen this figure again, I think it was in "a manual for men" or something like that. It showed an outline of an average penis, and various sizes above and below that, and gave percentages of each. I think the largest was 13 inches. But as you state, that seems pretty far out there. But the book mentioned that there are millions of men, and there has been thousands of years of people, who really knows what has been possible. I think the longest anyone has dared to claim has been 22 inches. Now thats even more far out there than 13 inches. But my god, what would one do with 22 inches? for that matter 13? It seems to large to even properly enjoy. Pain is what comes to mind for anyone having sex with such.
I think the largest I have ever seen in person must have been around 11 inches. I don't really know, I didn't measure, but it looked like 20! but when you realistically think of the actual size, it probably was between 9-11. In actual fact it probably was even 8. But an honest 8 is large! 9 or 10 is huge.