Sometimes they do rechecks to testtheir own systems. I think this started as a ramdom retest after the lab scandal about 5 years ago, where woman got clear smears only to find out years later that a few people in this lab werent picking up on negative results. Dont worry, if you got a clear smear you got a clear on.
It could be just a ramdom retest or a clerical error, maybe is should read April 2009!? Give the doc or nurse who did the test and see if they can explain, try not worry about it.