Very good explanation.
Many good points.
Fungible Tokens are common
Fungible tokens like pennies, nickels and times are produced in virtually unlimited amounts.
This means that all pennies, nickels or dimes minted this year are an unlimited number, we can always make more which are exactly the same in likeness and value.
So they are all considered common, and we would never refer to them as rare or limited additions.
Nonfungible tokens are limited in number.
Nonfungible tokens are produced in a fixed number, so there will only ever be 1, 10, 100, 1000 or some other fixed number.
They normally will never be made again
So they can be considered unique, rare or common.