Even if he had done something to the drive to make it encode the data in a different way so other drives won't be able to read it, they had his drive!
True... Of course, you might have a few values you poke into the C64's memory to allow you to be able to USE that modified drive... That would be a very unique take on password encryption! :-)
The short of it is, we just don't know. Of course, for ANY government organization to essentially come out and say they don't know how to use a certain type of computer simply because it is old...... That is remarkably disheartening. They should have contract resources available for knowledge on any technology they may encounter.