Naah, that may apply to SSD's, not to good ol' (rotating platters) hard disks, the magnetism does not evaporate.

The only issue that may happen on an unpowered for several years hard disk is so called bearing seizing, the (fluid) bearing of the motor/platter may become stuck, but it is relatively rare, though some particular make/models are more prone to this, and though (usually) fixable, in some cases it can be made to rotate freely again, but you need the services of a specialized service, as the disk needs to be opened, in some other cases the bearing can be replaced, and some specialized tools are needed:

https://hddsurgery.com/blog/hdd-motor-bearings

Thanks. :)

That reminds me of a work colleague a few years ago. He got an ancient drive working again by tapping it on the side with a screwdriver while powering it on, to get it "unstuck".

Not a typo, they've been powered off for around a decade. But HDDs (just like floppies) don't lose their magnetized property in just 3 years, or even 10 years, barring the very rare case of an extreme fluke or environmental exposure. Flash memory (memory cards, USB sticks, SSDs) loses electrical charge relatively fast, however. That might be what you're thinking of.

Thanks. Yeah, I was probably thinking of SSD's then. :)