If they were it means there are 1) Either no drives or 2) Nothing important. Unclassified means that any data that was on those machines was never classified or very long was classified and is no longer.
That aside, if these were gov related PCs, despite looking clean, I bet have paste that's drier than the desert. I'd take them all apart outside (bugs?) and clean them out. As fun as is spinning them is at high speed, tape the fans in place of you use compressed air as spinning them with said air will destroy them. Then repaste everything.
Do some stability tests and either sell them or repurpose them. Another option is donate them (if you didn't spend a lot) to some local non-profits or shelters or something.