could the head become degaussed simply over time and normal use
I am no audio expert, but I think an ordinary audio head must incur some residual magnetic just by regular use.
I wonder what happens during erase operation (write/format), as the erase coil is fed with VIN voltage. If it were AC (alternating current) that would demagnetise head itself, if it were DC (direct current), then it must magnetise it each time we write or format the tape?
Searching Google, there were long discussions about head demagnetization among Hi-Fi audio hobbyists, with unsure influence on playback quality, audible only by someone.
I have also read about a DIY demagnetise (degauss) solution, is to take a 12V relay, remove its coil core, place a soft iron core in place (ordinary thick nail), connect ordinary 12 VAC (alternating!) supply, put some soft protection not to scratch the head face, and apply for a few seconds.
But it sounds a bit silly to me, as I somehow feel unnecessary, but I stand to be corrected here by someone with sound knowledge in this area