With the exception of years that have only a couple of varieties, no one has been known to collect all the varieties for any single year. The challenge for a Single Date Set is simple: collect all varieties for any year of your choice. The toughest date to exhaustively collect would probably be 1870 due to the large number of double dies and design changes. It would also be challenging because the lack of nice specimens in 1870 make it a pricey year to pursue. About 39 varieties are currently indexed for this year.
Can you collect all the varieties from a single year? Have you done it? Champions and their sets will be added to this page in the future. It is rumored that David Poliquin may have put together a date set. Date sets are especially challenging because they are very much a moving target. Just as soon as you think you might be near completion, a new variety is found!
Another challenging date set to collect would be 1907. This year contains some 66 varieties, and more seem to be popping up every few weeks. The date series 1859 might seem enticing because there are only a few known die varieties for 1859. However, they are very rare. So good luck!