Modern drive heads are constantly reading the calibration data next to the user data and adjusting on the fly - an absolute necessity at current densities since

Modern drive heads are constantly reading the calibration data next to the user data and adjusting on the fly - an absolute necessity at current densities since minor temperature fluctuations would effectively destroy the ability to read or write data due to expansion/contraction pushing the head out of alignment. IIRC the next step is to put the logic for that in the head itself with a tiny processor so the feedback cycle can be nearly instant. I suspect that would eliminate issues with one head reading something written by another.