I don't believe "rare" or rarity is typically quantified. They're often one person's perception...and an arguable one, at that.
"Collectable" is another adjective of questionable worth. The common thought among my friends in this hobby is 'If they say it's collectable, you can be sure it isn't!' I tend to place "rare" with the same vain adjective attempts to hype salability. You know,...Caveat emptor!
I've never known manufacturers to be forthcoming with production figures to the hoi polloi. To do so would often foment an argument, rather than settle one.
I tend to think that the use of these questionable adjectives has little-to-no substantive value. For instance, one could say an item is "rare" when posted on Ebay for sale simply because the seller may have done a quick search of current or past activity for the same item and found very few competitive results. Or, just because the item is old...is it "rare"? (Actually, come to think of it, my wife sez I am, indeed!)
Anyone know if TCA has tried to quantify...legitimize...the term "Rare" being applied to this hobby's items?
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KD