Rare is a difficult term to define and I think this is a great way to describe your auctions. As you said, no one knows the exact quantity of the vast majority of this stuff. For all the years that the Internet was not used or even existed, folks were trading everything in person and print ads, and who knows how much of that was never documented on the internet. Online sales are not always easy to find, either. It'll be good to know about some of the very rare stuff having appeared at your place, just by the item's title. I'll add ultra rare and rare to my want list/ saved searches.