A minor point re: booklets. Would it be worth contacting the label specifically asking for permission to add them to CAA?
In addition, the label might be able and willing to provide a more machine-readable dump of their catalog, making imports even easier.
I’m planning to write to them directly on Twitter if they don’t react to my tweet about the cleanup today, let’s see 
The import script was updated following the discussion here and on IRC (version 2018.2.7)
I was in communication with them last year and have just written an email. Text is reproduced below:
Following our email correspondence last year [ …] I thought you would like to know that the MusicBrainz Community has decided to “clean up” all hyperion releases on MusicBrainz – in other words the end result should be a pretty complete database of all the label’s releases providing a very rich data set. See the process so far at Community Cleanup #4: Hyperion.
Hyperion is, so far, the only label to be selected for such special treatment and is partly because of your practice of making pdf booklets available so that the data is easily accessible (note that MusicBrainz will NOT copy the pdfs!). I hope that this is helpful to you. Speaking personally, one of the factors affecting my decisions on albums to buy is whether a good metadata set is available (assuming comparable recording/performance quality), so I hope the exercise benefits hyperion as well as the owners of your releases / other interested persons.
Of course, this does rather beg the question as to the entry of data for new releases after this clean-up exercise is over. As previously discussed, it would be nice if hyperion updated MusicBrainz for each new release (about 30 minutes work usually, once one has learned how to use the editor); then you would be able to claim that “all releases have a full metadata set on MusicBrainz” – do you have any further thoughts on this? (Meanwhile, I have just bought a bunch of releases and will be buying some of the new ones too, so will enter those in the database).
No reply received yet
@loujin asked if I could share a release that I think has everything for being marked as high quality as an example, so: this is what I think we should try to get, pretty much.
I’ve added a piano technician relationship since I’m seeing this credit a lot. No need to throw it in the annotation anymore!
Since this credit should also be used for piano tuners, is it the same thing? What does a “piano technician” do apart from (presumably) tuning the instrument?
“piano repair, piano tuning and piano appraisals” says the Piano Technicians Guild. So in our case, mostly just tuning, I imagine.
I guess it is basically a piano tuner, but there is a lot more to it than getting the pitch right. (I recommend watching Pianomania for a fascinating insight into the work of a piano tuner with some very exacting concert pianists.)
Is there anyone (@loujin?) who has a simple way to change all the vocals in this release to choir vocals? It also needs fixing all the German caps, I guess…
Somewhat belatedly started to go through hyperion, starting with my collection. This one: https://beta.musicbrainz.org/release/f6494838-5c49-4b56-a526-c9eae90c27f9?tport=8002 was also available as two separate CDs (which I have) - https://www.hyperion-records.co.uk/dc.asp?dc=D_CDA67307 and https://www.hyperion-records.co.uk/dc.asp?dc=D_CDA67308
but I’m not sure how that should be dealt with in MB - should they be shown as two separate releases under the same release group and is there an easy way to create them from the double-CD?
They should be two new releases in two different release groups.
You can add an existing medium to a release from the Tracklist tab (Add Medium > Existing Medium). Unfortunately the search thing doesn’t allow searching by MBID (must me the only place in MB where that is impossible!). But if you search for the exact title and release artist of the existing release, with the same number of tracks, the first two results are actually the media you are looking for.
Also, don’t forget to set the “included in” relationship to the release groups!
In fact I was wrong - the separate releases have already been entered - twice for vol 2! I added the “included in” relationship to https://beta.musicbrainz.org/release/c4816fc2-c685-47af-bb89-a83b5c7b9e62 before I realised it had two entries. Then I saw that the other entry (edited by the redoubtable @reosarevok ) used a “part of” relationship to the series https://beta.musicbrainz.org/series/7c46a6a9-22b9-4b58-afcf-47f1bf46fd22. Should there still be an “included in” for the releases?
Also clearly the double entry needs merging (not something I feel confident in yet - still learning!).
BTW, the reason I didn’t spot this at first was that I was running Picard on my collection to find the matches and it got this wrong. However, @loujin’s excellent script quickly identified them all 
Question re track titles:
Guidelines say
When a release has titles in several languages (for example, English / German / French), enter the tracklist in the main language of the release. If all languages are given equal weight, just pick one. The others can be entered as pseudo-releases and linked to the release marked as official with the appropriate relationship.
However, this one: https://www.hyperion-records.co.uk/notes/67895-B.pdf seems to indicate to me that both languages should be included in the title. The booklet has the Czech title in italics. How to show this? ‘English - Czech’? ‘English (Czech)’? ‘Czech (English)’. If I omit the Czech it will be lost entirely (as the works are entered in English, rather than Czech with English alias).
IMO yes. This is a (small!) series of standalone releases, which also happens to have been released as one set, so both are true
I’d do English only, with a possible pseudo-release with Czech only (as by the second sentence you quoted). Hopefully soon we can actually just turn the pseudo-release into an alternative tracklist for the release instead, but that’s not quite here yet
That’s done at https://beta.musicbrainz.org/release/b393b490-ccd2-43b4-972c-04114d472539 and https://beta.musicbrainz.org/release/9900e234-a599-4500-be40-258e8eab229b
Hope I’ve done it right. I must say, it seems rather clumsy to me.
It is 
That’s why I’m hoping we’ll get the proper alternative tracklist stuff soon (it’s been half-done for a year or so though…)