What is "Rare?"

Warren's recent post discussing how rarity has changed over time was very interesting. I read Wilson's "Western Bitters" for decades, and my impression of desirability was molded by this book. It's numerical "weight" was pretty innovative in it's day, and most of the bitters in this book have retained their desirability compared to one another over the past 40 years! I also found it interesting that there are 19 or more variant 2 Cassin's Grape Brandy Bitters in collections. This was considered an "extremely rare" bitters in 1969, and while there have been more examples come to light, the demand for this bottle stays strong. I would be very curious as to how many of the 19+ are near mint to mint. They are so prone to damage, it is incredible that they can be dug up and be perfect. The Wonser's Bitters seems to have strong demand though there have been quite a number of amber examples sell in the past 10 years. It seems that the values remain strong. This indicates there are fewer bottles than collectors who want them. According to Warren's count, they are a very scarce bottle, but not rare. Again, I wonder how many are mint or near mint. I see the word "whole" or "intact" when counting specimens. One bottle that held a very high numerical weight in 1969 was the Wormser barrel shaped bitters. These appear to have fallen a bit in desirability over the years for some reason. Why? They are very scarce, and colored, and have a nice shape. Barrel bitters are passionately persued by collectors from coast to coast...maybe it's because they do not come in green or aqua, or puce? I have noticed that so far in the 2010 Spring digging season, there have been some killer whiskeys dug, but I have not heard of even one top bitters being unearthed this year...maybe I am out of the loop.