This is what a lot of people overlook - when the court compels you to produce evidence, or ill gotten gains, saying ,"I can't" - isn't a legal defense.
We're getting closer and closer to testing that. IANAL but I'd imagine that some combination of the 4th and 5th amendments should cover that situation. The onus would be upon the prosecutor to prove that you destroyed the evidence after the fact.
As a general rule, one does not have to prove they didn't commit a crime, the prosecutor has to prove that they did. Where this gets murky is if a judge orders you to present the non-existent data as contempt of court may apply.
As such, would you please explain why you provide a timeframe for keeping the data prior to deleting it?
Where I work, we delete emails older than 6 months as a company policy. I have to assume this is done for exactly this reason. Don't ask why we might want to do that, I'm not in charge. :-)