Probably A Dumb Question...

It's a lot easier to know how many notes there are then coins. Each note is unique in its SN and design. Some people use this to make a profit, other use it in an attempt to educate. You are correct tho, no way to truly know exactly how many there are still in existence. I think it keeps things interesting.

Although using the rarity estimates established by TPG's has some value it is important to remember that the actual price an item or currency sells for well NOT be because of the old "supply and demand" adage.

If you are searching for $1000+ value notes the number of people able to afford that level of purchase is significantly lower than those who can afford to spend $100.

So although you might have 10,000 ACTIVE currency collectors there is probably only a small percentage of them who can afford the higher value items.

If there are only 10 known examples of a particular piece but only 5 buyers able to pay the current price for one of those available issues, one of them pay sit for some time before they actually sell.

The price is not determined just by supply and demand, but by the ability of the collectors interested in a piece to afford that level of collection.

As an example, if a rare item worth $50,000 is offered for sale, but the only people who see the offer could never afford a purchase at even $10,000, then it may be quite some time before a 'high roller' finds and wants that item.

Rarity must be compensated by price level as well as interest.

Well said, amrys. Small-size paper money collecting is still in its infancy. There are staggering numbers of raw high-grade notes of all denominations out there, and multiples more of circulated "kinda funny looking" circulated notes that people have stashed away.