Okay, here's a book called "All You Need to Know About the Music Business" first published in 1991 by a recording industry lawyer (a guy who would have been involved in writing those contracts). It contains the passage:

"The word master has two meanings:
1. The original recording made in the studio is called a master, because it is the master (meaning controlling entity) from which all copies are made (the machines making the copies are called slaves—master/slave; get it?).
...
2. The word master also means a recording of one particular song. Thus, you might say an album has “ten masters” (meaning ten selections) on it. These individual recordings are also called cuts, because of the historical fact that each selection was “cut” into vinyl."

You originally said:

"This terminology was incorporated into software, back in the CD-ROM days, with their "gold master" from which copies would be produced."

So it appears you are referencing the first usage of the term master, which this industry insider explained in 1991 (a pre 2020 source) had a direct master/slave relationship to the copies, and the terminology was used knowingly to refer to a more conventional understanding of a master/slave relationship between humans.

This master/slave relationship between recordings seems to have been used in other contexts in the industry, showing its usage was widespread.

Here is a retailer explaining in 1998 what a "slave" reel is (in contrast to a "master" reel): "Historically refers to a reel of multitrack tape upon which there is a submix of the tracks from a “master reel” to record overdubs against. The purpose of slave reels is to more easily provide additional workspace (tracks) for creating multitrack recordings." https://www.sweetwater.com/insync/slave-reel/

Here is a machine from 2002 called a digital loop bin that duplicates "slave" tapes from a master: https://web.archive.org/web/20030318000601/http://www.optica...

Here is an account from 2000 by someone who worked with the analog version of these machines in the 70s. He uses the terms "master" and "slave" throughout: https://web.archive.org/web/20101208122537/http://www.8track...

Here is a post in a large community of audio enthusiasts about a recording from the 80s labeled as a "safety" for a master and slave reel. If you search on this site you can see the words master and slave used in various contexts from master/slave recordings to master/slave sync relationships: https://www.gearslutz.com/board/so-much-gear-so-little-time/...

So to summarize we have:

- Accounts by several prominent artists of encountering master/slave terminology referring to recordings, both in common parlance and in contracts.

- A popular book (10 editions, 500k copies sold) written by a prominent recording industry lawyer, who would have been involved in writing contracts, that explicitly defines master recordings with respect to slave recordings. He even gives a wink/nudge to the common understanding of a master/slave relationship in human society.

- Various technologies that through the decades were advertised as having the capability to make "slave" recordings from "master" recordings.

- A community of audio enthusiasts who have incorporated master/slave terminology into their parlance.

Given this evidence, can you please explain to me whether you are still "fairly confident that master/slave terminology wasn't used by the recording industry"? What would it take to convince you otherwise?