The means of identification on magnetic tapes is shown in the magnetic tape file specification User Guides.
Magnetic pockets have magnetic tape to the top edge so they can be simply lifted and relocated when necessary.
Another great idea is to apply magnetic tape to the back of each puzzle piece, and place the puzzle on the fridge for little hands to do.
Consider laminating it and backing it with magnetic tape so that you can stick it on your fridge when you go out.
Later, the world of electronics allowed the conversion of sound waves from a microphone into "electromagnetic fluctuation" that gets imprinted into magnetic tape or, in the case of today's digital recorders, a digital memory chip.
