In this thread (which began on the 4th of April 2011), we started with 2011. On the first day, members posted all their coins from 2011. The next day, they posted 2010 coins. Basically, we go back one year per day. If one year is not posted, the next cannot be posted until someone posts it (basically, we can't skip any). You can post a coin into the next day as long as no coins of the next year back have yet been posted. Members on this thread have posted coins for every year going back to 1494, and now we're waiting for 1493 to show up.
Basically, unless you have a coin that's dated 1493, you can just watch and wait.