A comment on this question raised another interesting question, specifically this comment:
If they kept it in 1999, they'd have no y2k bug to deal with.{/tongue-in-cheek}
And it got me thinking...The Matrix is a simulation of the year 1999. Everybody in The Matrix thinks that it is the real world, and pass their lives as if it were exactly that.
But if that is the case, it wouldn't be 1999 forever. Years pass. People keep track of time and have children that grow up and have birthdays. They're going to keep track of what year it is.
Will it ever be the year 2000 in The Matrix, or do the machines 'reset' people's memory of what year it is, so that it is perpetually 1999?