Although otaku (nerds, basically, of manga comics and anime in the main, though not exclusively) are not shunned by polite society these days, 30 years ago in the Showa era it was a different kettle of fish. This survey from goo Ranking sheds some light on common knowledge from 30 years ago that is unbelievable today.
Note that the demographics for the survey is for people who at the most would have been ten years old 30 years ago and have grown up with manga and anime being mainstream, so perhaps they were hearing much of this common knowledge for the first time when answering the question.
Also note that although manga and anime are the main focus, computer otaku are also covered by some of the questions.
In number 2, most foreigners seem to still use the term Yaoi, but I’d never heard of Doujinjo, so I wonder how much they were reacting to the second term rather than the first, or is it just my lop-sided knowledge?
In number 12, I have absolutely no idea what sanding down varnish has to do with anything or why people can not believe that was done.
I searched for vintage manga and this came up: