Just left a rarity estimate for these. It reflects overall availability based on over 20 years of recorded observation, but there are four varieties (five if you count a minor subvariant that is also the rarest) ranging from few known to the several times a year that I assigned. Long-term average of all types on ebay is about once a month, but some of the varieties exist in fewer than 100 units, so are rarely seen. I should also note that at this point, the market generally does not make distinctions in value between the types, but that may be because the variations are largely unrecognized within the market.