1) They keep in the database old records.
2) don't delete records automatically
3) from the website:
"Third and finally, if you are really not a spammer, or you are truly reformed, de-listing is relatively easy. You donate US$50 to a charity or trust approved by, and not connected with, SORBS for each spam received related to the listing"
In other words blacklisted guys won't be able to send you emails unless they pay $50, what won't happen. It is really hard to get delisted there.
My advise is to try