A release group seems to have been created as grouping mechanism for a series of 32 CDs.
Release group
https://musicbrainz.org/release-group/2d8eeffe-e138-3cc5-8e8a-875544bcf28c
How do I move the grouped releases into
https://musicbrainz.org/series/5616c07a-d818-49ba-ae99-59c641d81cf7
?
It’s not as obvious as relating the release groups to the series because there is only one release group for all ~32 releases.
You should add separate release groups for all (yes, that’s kinda slow 
). You can add them to the series while you’re creating them at least, you don’t need to wait for the edits moving the releases to pass. But anyway, if you do it, let me know when you’re done and I’ll check and approve the edits 
Series below has been filled with release groups.
https://musicbrainz.org/series/5616c07a-d818-49ba-ae99-59c641d81cf7
Can’t see how to form a release group relationship between, say, release
and release group
You need to edit the release, and paste the new release group in the “Release Group” field
But … but … I was expecting to have to learn Python or something codey.
Heh. There’s very little that requires coding abilities to use MB - there’s a lot that can be made easier and quicker with scripts, but
Each release has now been related to it’s new release group.
Still some tidying to do. Like,“Masters” insead of “masters”. 
Save the best for last.
It’s looking pretty much that this series currently titled,
"Masters of the Roll: Rare Original Recordings From the Reproducing Piano by the Great masters of Classical Piano 1904 - 1935: A 32 CD Catalogue"
is better re-named to the original serie release name of,
“The Condon Collection” .
Sample of release:
Example of series name being used at Katalog der Deutschen Nationalbibliothek
https://portal.dnb.de/opac.htm?method=simpleSearch&cqlMode=true&reset=true&referrerPosition=3&referrerResultId=intRef%3D118596721%26any&query=idn%3D340025611
Problem is that not all tracklists are available. So far. the ones that I 've checked do match.
I can only concur with mmirG.
In my humble opinion, this naming is completely inconsistent with the guidelines.
Another example: “disk 1” can never ever be part of a release (group) name.
This should be a property of the songs.
Not always true Sometimes it’s equivalent to “Volume 1” after all.