My aunt used to head up the accounting department at London Records and I once asked her who owned the master tapes, she said that varies from artist to artist, even contract by contract for an individual artist. She also said that she remembered, at times when a pressing was beyond end of life, they sometimes had to remaster an album, so they could recut the pressings.
Washington Post article on MoFi vs. Fremer vs. Esposito
Here's a link to a Washington Post article on the recent dustup with MoFi. The comments section (including posts by Michael Fremer) are interesting.
Disclaimer: This is a "public service announcement, a point Im adding since some forum members complained the last article I referenced here was "paywall protected", I'll note that, for those who are non-subscribers, free access to limited numbers of articles is available by registering (trade-off: The Post will deluge you with subscription offers)