It is an entry for "1992" not as a calendar year or a number but in another meaning it acquired in relation to the introduction of the single market.
1992 is listed in the Oxford English Dictionary (online):
"The year 1992 as the year in which a single market was due to come into operation within the European Union. Cf. single (European) market s.v. SINGLE a. 17a. Although scheduled for 1992, the single European market did not in fact come into operation until 1 Jan. 1993."
On the page 1992 there is a link to a newspaper article where "1992" is being used in this way to refer to the year the common market was due to start.
It is on one of the 'missing word lists' and there is precedent for entries whose titles consist of digits (0-9) rather than letters such as:
and many more, see Category:Arabic numerals (which was nominated for deletion several months ago ([http://en.wiktionary.org/w/index.php?title=Category:Arabic_numerals&oldid=4114394|14:14, 15 April 2008]) but has not been deleted.
Most of these you will not find in the Oxford English Dictionary but you will find "1992".
I expected this addition could be controversial but I am prepared to defend it and let the community decide.
My inclination would be to move to RfV. But what kind of quote would count as attestation? The gold standard for attestation would be that in a given work at the first mention of the year in running text (excluding a teaser first paragraph?), it had not yet been specified what specific events of that year were referred to by the use of the year. Other example of years that might merit entry would be 1776 (US), 1492 (Western hemisphere), 1066 (UK), 1929 (finance, economics. banking). Perhaps 1945. One distinctive thing about "1992" is that it was in widespread use referring to the harmonization well before 1992.
I think it is the way 1992 is being used that is important (for dictionaries) rather than the fact that important things happened in 1992. There are two key differences in usage:
(1) 1992 continued to be used even though the process was a year late
(2) 1992 was being used as a noun referring to a process rather than to a year. e.g. you don't respond to 2009 you respond to 'events of 2009'
"The response to 1992 by individual countries has generally involved competitive interaction between domestic governments and regulators to ensure that..." International regulatory rivalry in open economies: the impact of deregulation on the US and UK financial markets
"National restrictions that would limit the free circulation within the Community are not compatible with 1992, so these national restrictions must disappear..." The Impact of Europe in 1992 on West Africa - Page 60 
Keep This is a proper noun, referring to an event. It actually took place in 1993, so the term couldn't be any more idiomatic. OED's best quotation is “The second component of the Canadian response to 1992 is the ‘European Trade Policy Strategy’ . . .”, but I haven't found an independent source to quote. —MichaelZ. 2009-08-09 20:32 z
I'm also thinking keep, now that the entry has had a good ol' cleanup. See also the current WT:BP discussion. Mglovesfun (talk) 20:35, 9 August 2009 (UTC)
Move to RfV for attestation. DCDuringTALK 20:55, 9 August 2009 (UTC)
the general view seems to be that although my initial explanation was not great this should not be deleted.John Cross 21:36, 13 August 2009 (UTC)