What we did was to take our customers active on a Sage or Schulz agreement. I'm not convinced of the value of the customers off-plan -- though if they are on an agreement with us we took their data.
I've had very little exposure to these older customers coming back as most seem to be legacy ""was a good ft when MAS was $ 799"" types.
We took all active customers, their unlock keys, as well as plan info.
We also took info for anyone not on maintenance but on a Schulz Agreement