They are technically rares. A long time ago you could create multi-gem jewelry, all gemstones. You could make bracelets, earrings, rings and necklaces, The highest amount a piece could have is 60,000. Their value seems to be based off mainly their stone count with matching gemstone count jewelry sets of 4 or 6 worth more. One popular theme crafters made were "year" sets, which is what you have. Other include stuff like 666, 69 and then the more rounded ones like 50, 1,000, 10,000, etc. You had to have the amount of gemstones on you to make the number you want, but when you actually crafted it luckily only used one gem. This was back when gold was significantly more expensive than today (I recall around $50 a million about that time) and so the highest counts were harder to find because of the upfront cost... not to mention the respawn NPC wait as there wasn't the set 500 back then.
With history lesson finished, I base prices on the gemstone count. What I usually sell the individual 1k-2k pieces for is around 250k each. You might be able to get more with the sequential numbers, but I don't know what sort of attraction that has for folks.
Hope that helps.