The old rule (governing prizes from 1993-2004):
Any research paper or a series of papers published (not reprinted) in a recognized refereed journal by a single author or a team of authors in the seven years preceding the year of the award is deemed eligible.The new rule (prizes awarded 2005 and later):
Any research paper or series of research papers by a single author or by a team of authors is deemed eligible if the paper was published in a recognized refereed journal before nomination but the main results were not published (in either preliminary or final form) in a journal or conference proceedings 14 or more years before the year of the award.So, two key changes: firstly the clock starts at the time of conference publication, not journal publication, because "it often is the most effective means of bringing the results to the attention of the community". Secondly, and of course this is related to the first change, the time before eligibility expires has increased to 14 years.
Which means that there is now time for the amazingly cool paper on embeddings by Linial, London and Rabinovich (published in FOCS 1994, and in Combinatorica in 1995). Maybe it's already been nominated... ?
p.s Given the limited eligibility period, it seems that giving out more than one award each year might account for bursts of inspiration where more than one seminal paper gets written in a year.