The relative scarcity of older coins in good condition is a function of many factors, the economic environment being one.
The value of a coin is a function of its scarcity for its type and condition, and the number of collectors seeking an example.
However the local Irish economy has been through a significant boom which must be an additional factor.
I am inclined to expect the MS65 prices to stretch away from the MS63 prices over time driven by the US market with its dependence on 'slabbing' and precise (albeit inflated) grading.You'll go a long way to find somebody who'll crack a slab to resubmit a coin that they think was overgraded.This pretty much ensures that any coin will eventually get graded up as high as reason will stretch it.The rarest coins in the world and the most expensive coins are not the same.Naturally the most expensive are not particularly common, but it is certainly true that obscure but extremely rare coins (even unique examples) can be quite inexpensive.At the moment (Jan 2001) the most expensive coin (in terms of realised auction value) is the US 1804 Dollar which sold last year for just over ,000,000.00. Since I wrote this the only 1933 US double eagle has exceeded this price, but the comparison with the Irish coins is still valid.An Irish halfpenny of Edward III of which only two examples are known sold at about the same time for about ,000 and and Irish penny of Henry VII again one of two known examples sold for 0.) are rare because of Central Bank decisions rather than normal circulation issues.And several dates in the 1940s, 1950s and 1960s are surprisingly rare or common for some denominations considering their mintage.So you really do have to get into the habit of judging the coin itself and not the slab it is in.It is a general rule that any dealer that sees a coin in a slab with a lower grade than he/she thinks it deserves will crack the slab and resubmit it in the hope of getting a better grade.