The links you provided are for sure useful. I know this has been discussed in the past and you have provided some good references.
My intent in this thread is to derive some sort of guideline that can be stated clearly. Something like the 4 bullet points I posted above, in format, not content as my words may not be correct. I understand it is never that simple, however, I believe it is possible to generate a general guide that will help for the majority of releases. I also have no personal knowledge of such things in other countries, so that is a part that I am not aware of how to address.
From my understanding the copyrights are in a similar boat as the ISRC. It is heavily tied to money - the who gets by who and for what. With that, I can understand, as some have stated in the ISRC discussions, that they have no interest in them. From my side of things, this is of interest to me, although I do not use it for the tracking of money. As I have stated prior, I have a great deal of interest in the mastering process and personally consider them different, one master to another.
While the courts in the US have recently made a more firm statement on this, the (p) information can assist in identifying specific masters of a recording. For this to work though, it needs to be tracked in the data being used as reference. Say I have a CD (p) and (c) by ABC. Later, there is another release, of the same, but with (p) and (c) by XYZ. I assume that most would consider these two releases to contain the same recordings. As MB does not distinguish further into the recording, this makes sense. However, a new (p) copyright can be issued if there are differences that MB does not track.
Using words that are not mine:
The first right held by copyright owners is to reproduce the copyrighted work via printing CDs or vinyl, and make the work publicly available via streaming services. Technically, every time a listener presses play on a specific song on a streaming service, they are triggering a reproduction of the sound recording (aka the master) AND the underlying musical work (the composition).
So, streaming services must have licenses from copyright owners to reproduce any songs in their catalog. Master copyright owners receive compensation via streaming payouts, while composition owners receive mechanical royalties.
While that statement centers on streaming, the concept is the same in the sense that you can hit play on a CD, digital file or a streaming service all the same. But I hope it shows how a different vendor can be differentiated by such things.
I hope I explain enough why my interest in the topic and how I do and intend to use the information.