The master tapes are just that: the final mixed sound and outputted to audio tape.
On a production back in the days, you had your on set sound recorded on a nagra and all of this was edited and put to stems which is multi tracked tape. One track was dialogue, another was music and another was sound effects. These stems are then mixed and mastered to stereo, mono, surround sound master tapes.
I understand that but didn’t all the played audio in the film prints come from the film (on the side)? Or where else someone could get these master tapes unless working for LFL? Just wondering is this a similar case to “I wish we had the o-neg to scan it for OT.com members” or are these tapes actually around somewhere like film prints?