Sometimes I see printed on releases:
℗ & © XXXX ALL RIGHTS RESERVED
Where XXXX is a year date.
When having a label name instead of an ALL RIGHTS RESERVED, we can set phonographic copyright (℗) and copyright (©) release-label relationships with start=end=XXXX.
Missing these relationships, I miss the copyright dates.
Especially interesting when I am often missing the release date.
But how to set it, in this case? 
Thanks, good idea! 
I queued edits for the release I was editing with this issue: https://musicbrainz.org/search/edits?auto_edit_filter=&order=desc&negation=0&combinator=and&conditions.0.field=editor&conditions.0.operator=%3D&conditions.0.name=jesus2099&conditions.0.args.0=285909&conditions.1.field=id&conditions.1.operator=BETWEEN&conditions.1.args.0=81905943&conditions.1.args.1=81905996
[no label] is not the same as [unknown]. Obviously there must be some kind of record company or production company holding the rights…
It’s a self produced record.
The covered works do have publishers, yes (only writers are credited on the package, though).
But the recordings and the release, I’m not surprised there is no companies.
I think [no label] is more appropriate to this specific case.
I would have thought that is the artists reminding you that they own the copyright. I’d assign (p) and (c) to to Mike Greene & Youssef Remadna as they are the people you would need to talk to about using the product. Especially as it is self produced and not on a label.
Maybe I should links artists instead of special no label, yes
But here is not about the works but about the recordings and release.
It’s mostly a cover album (except 1 original work).
I generally read it as the (c) is to who made that compilation, and the (p) is who has rights to those recordings. In this case I would expect that to still be the artists doing the performance.
Maybe check a few other CDs of cover versions. I’ve had a quick poke at a few and the don’t have dates of the original Works as each would need a separate original date if that was the case.
(I am no expert, but working on other examples)
According to Sound recording copyright symbol - Wikipedia “if the producer of the sound recording is named on the phonorecord labels or containers, and if no other name appears in conjunction with the notice, the producer’s name shall be considered a part of the notice.”
(c) generally refers to the artwork/graphic design/packaging design. For compilations, you will often see “This Compilation (p) (who made the compilation)” on the back cover. Sometimes you’ll find recording information in the booklet, but more often than not, I see song/work publisher information rather than recording information.
So we come back to the two Performers again as they produced the music, and produced the packaging.
Interesting. So everything visual and physical about the package, but not for the music you hear.
Again this seems to come back to the two artists would be the (p) and (c) in this example?
The relationships are also available for artists, indeed.
I did not use artists, at first, because I thought it was a little bit more of a guess.
What I like with [no label] is that I can say it is credited as all rights reserved, I can mimic the packaging text.
And this all rights reserved thing is quite a recurrent text on [no label] releases or some compilations.
Still thinking… 
But the copyright is not for some entity “all rights reserved”, also “no label” is literally no label, and that kind of comes down to “copyright nobody”, which is for sure wrong.
As an creator you hold the copyright on your work, so if not said otherwise the artists would hold the phonographic copyright indeed. For the copyright on the physical release probably more people are involved, such as the graphic artist(s).
If in doubt I probably would just put it into the annotation.