The Lifetime of a Lead

My understanding is that you should contact a lead every 30-60 days; but, for how long (assuming they don't ask to be removed from your list)? I was thinking the following:

1. Preforeclosure - Until they get foreclosed on or 6 months goes by

2. Probate - Until they sell or one year goes by

3. Absentee - Until they sell or forever (?)

4. Tax Liens - Until they are forced to sell or get caught up on payments

5. Code Violations - Until condemned or brought up to code

What do you guys think?