It doesn't matter. Providing a PIN that will cause an officer to inadvertently delete data clearly is covered by the statute:

"Whoever, before, during, or after any search for or seizure of property by any person authorized to make such search or seizure .. takes any action ... for the purpose of preventing or impairing the Government’s lawful authority to take such property ..."

My understanding is the duress pin deletes encryption keys, but leaves the property untouched.