If this is off your credit report, paying it will not place it back on. I would point out to you that paying this will not do anything except make you feel better, and possible reset the SOL on any outstanding balance.

First, the SOL claim:
Let's say that you owe $1,000 on this account, and they get you to pay (or even promise to pay, in some states) $100. You have just reset the SOL and can now be sued for the other $900. Keep that in mind.

As far as paying what you owe:
This debt is likely in the hands of a Junk Debt Buyer (JDB). JDBs are a type of collection agency that buys debts for pennies (or less) on the dollar. They will buy $10,000 worth of accounts that are out of SOL (called junk debts) for $100 or less. Then, if they get even one person to pay, they make enourmous returns on the initial investment. So, if you pay in this case, not one penny will go to the person you failed to pay, and you will only make the JDB some profits.

If you want to pay because you have a guilty conscience, send an anonymous money order to the original creditor (apartment complex). At least that way, you can clear your conscience without enriching a person who didn't lose a dime in the transaction, or entangling yourself in SOL issues.