The biggest factors in why the prices are going up so fast are, 1) you can only get the "20th Anniversary" labels on the three coins sets if you send them in to NGC or PCGS in the original, UNOPENED boxes from the mint. Most people didn't know this when they first received their coins and opened them to admire them, or make sure they got them, etc. If they did this, then only the reverse proofs could get the "20th Anniversary" label. This lowered the total number of graded sets that will be available now and into the future. 2) The number of new collectors of the
ASE series has increased dramatically in recent years. All these people need the three coin silver set in order to have a complete set. Whether it's graded or not, there are only 250,000 of these sets out there. There are a lot more than 250,000 collectors, so the supply and demand aspect takes hold.
The NGC 70
ASE sets are selling for upwards of $1,800 on
ebay right now, with the 69's are going for around $600. That is a huge difference, but the difference between a 69 and 70 is huge in collector's (and seller's) eyes (even though most people could never tell the difference between the two!).
Here are links to the NGC census pages for the
ASE's, both MS and PF. This will show you why the 70's are more expensive. The majority of coins graded are 69's, with only a few from 68 to 66.
http://www.ngccoin.com/poplookup/po...signation=PFhttp://www.ngccoin.com/poplookup/po...signation=MSAnd here is a page from Heritage Auctions showing the PCGS numbers (though I don't know how up to date they are, since it shows nothing for the NGC grades which are listed above from NGC's website):
http://coins.ha.com/common/view_ite...10156&src=pr