[Jedd]

Not terribly informed about the pressing process, but as I understand it, it is (or was) effectively a player-process in reverse.

A needle creates the groove(s), replete with bumps for sound, in a not-quite-set (slightly soft) master disc - and I _speculate_ those follow a specific path defined by the mastering tool.

In comparison, playback just drops the needle in the track, and it necessarily follows the extant spiral form.

Making the master of a multi-groove record I'm assuming would require recalibration of the groove-defining mechanism (doubtless carefully designed for conventional layout), once for each of the grooves you want to make, ensuring they each stay within the boundaries defined by the previous grooves.