It's very easy for moderns to forget (or just not know) how difficult it was to find information before the Internet really took off.

When Ken cited "Unknown Air Force Document", you can be sure it would have been a direct citation if he had the paper at hand. But let's be generous and assume he called an Air Force reference librarian and described the paper he was looking for, and said librarian wasn't able to find it on the basis of that description. What's the next step? There isn't one.