As some of you know, I have had a fairly broad knowledge/experience in the coin hobby before becoming hooked on casino chips. The question of "rarity" is defined in different degrees in the coin hobby depending on the particular type of coin. I specialized in bust half dollars prior to 1836. According to the well respected reference works on that subject, "Early Half Dollar Die Varieties" by Al C. Overton, the following rarity scale and definition was pretty much universally accepted by collectors of this particular series of coins.
RARITY: "Each variety is given a Rarity rating of R.1, R.2, R.3, etc. The method used is a simple one, each R number representing a specific estimate, based on observations and records covering many years."
R.1 Common over 1000 (estimate known... not issued)
R.2 Slightly uncommon 500 to 1000
R.3 Scarce 201 to 500
R.4 Very Scarce 81 to 200
R.5 Rare 31 to 80
R.6 Very Rare 13 to 30
R.7 Extremely Rare 4 to 12
R.8 Unique or nearly so 1 to 3
I don't know how this scale fits in with each persons own description of rarity... or if it is even close. However, when determining value, with "rarity" goes another factor called "condition" (or if you prefer, "grading). What a can of worms that subject opens up no matter what collectible is being discussed. I don't know that we even want to go there. For whatever it is worth for the purposes of this BB discussion, I submit the above for conversation. Archie