From my very long experience with various HDDs, a year is too short, I'd say refresh data every 2-3 years or so. IMPORTANT data needs to be on 3 different backup storages, also preferably use different locations (your second/third house, for example). If you have something to hide, then NOT your house, obviously. I even used to store data in a very humid enviroment (with the measures taken). BUT 12 years HDDs (if I read your post correctly, they were constantly on) - the only place for them is a dumpster, sorry, they aren't safe to store anything on them. Don't buy the new ones from Toshiba, and don't buy the ones that have the "new" crappy SMR tech, like WD60EFAX or any Toshiba model.