Hi

It is a great mistake if one thinks about 0 and 1 in today's digital equipment. A digital signal is represented by voltage levels, magnetic induction vectors, these are pure analog signals. The equipment has to treat these signals properly to interpret them as 0 and 1.
In really high frequency areas the signals have to be conditioned, filtered, etc to be able to carry the information.
so please do not think about a bit of magnetic matterial being 2 state.
If U are thinking of a processor or a PC motherboard, U think of digital equipment, but it is much more complicated, designers have to take care of the signal's distortion, interference and some other things to make them work.

Besides I can hardly imagine anyone has equipment to recover those erased bits

pepe