Easily done in analogue days with two heads mechanically seperated by a tape distance equivalent to one disc revolution in time on the master tape replay - and the quality of the preview signal (head, electronics etc) doesn't matter much as its only purpose was to tell the system that high cutter excursions were to be expected one disc revolution later, so that the traversal servo could be speeded up. The quality of the main replay head and subsequent electronics remains unaffected.

Much the same sort of problem as when adding tracks to a multi-track master: the required characteristics of a record head are quite different to that of a replay head, so that when adding tracks one listened to previously recorded tracks via the record head to maintain time synchronism - and lived with the poorer quality reptroduction - and then listened later to the overall result for mixdown etc via the replay head.