Coins more rare than RIC lists them?

[Ghengis_Jon]

Allow me to toss this out for argument's sake. 

I just bought a Constantius II 'twin victories' AE4 from victoriaecoins (thanks Joe!) with a mintmark of  SIS .  Rated c2 by RIC.   There are 5 variations of this specific issue, 2 of them rated c2 and 1 rated as c.  Going through my collection, I have 103 coins of CII struck in Siscia.    These coins have come to me over several years from different sources.    I watch a number of internet auction/sales sites and this was the first one I've seen pop up.   So why haven't I seen at least one before?  If it is possible that as what was once considered rare by RIC is now found to be common, can it also be what was once considered common is actually rare?

[PeterD]

The RIC rarity ratings relate to specific collections, hoards and catalogues. It's quite possible that the majority of specimens of a particular issue come from one hoard in the dim and distant past which ended up in, say, the BM and are still there today, but that no more finds have come up since and so they are still rare "in the wild".

[Lech Stępniewski]

Peter is quite right. Let us assume that on the whole world exist 100 specimens of a coin X, but every major collection has one. According to RIC coin is common (noted "in every major collection"), because "RIC rarity" IS NOT "market rarity". There are many coins rated common in RIC, which are rare on the market.