If a release contains only classical music but it has a conventional Pop/rock type tracklisting (such as Michael Nyman film soundtrack) do we still use CSG ?
If you have a recording on multiple releases, some using CSG and some not what should be stored as the recording artist?
Right now soundtracks have a separate style, although weāve had a couple discussions about maybe simplifying it into āuse CSG for score/orchestral soundtracks and normal guidelines for pop onesā.
Other than soundtrack stuff (see above) I havenāt seen that happen often. When I have, it was mostly a classical track being added to a random compilation, in which case Iād use CSG because the original album probably requires it.
Thanks (I didnt see it because its not listed in the contents of Style - MusicBrainz - although I see there is a link to it at the bottom)
Okay, I ask l because if I look at the list of recordings made by any long deceased composer such as Bach Johann Sebastian Bach - Recordings - MusicBrainz (160 pages) there are many recordings attributed to them, and from the guidelines shouldnāt there be none. I realize there is plenty of work to do on the db but that sounds like rather alot of recordings to me
It is there, under āSpecific types of releasesā 
You answered your own question It takes ages to clean up a big composerās recordings - the biggest Iāve finished on my own was Messiaen, which had like 40 pages back when those were 50 recordings (theyāre 100 now IIRC). Someone like Bach is almost impossible to clean properly without an organised community effort (and a fair amount of the albums for people like Bach are there since the early FreeDB days and have no info at all on who performed them nor any edit notes with info 
).
My bad
True, but the guidelines say 'If no performer info can be found, use āspecial artist [unknown]ā so I suppose it would be more correct to just batch change them all to that as a starting point, at least that might push towards the right way to edit them.
It would also prevent the to my mind a misleading aspect of the UI that if you click on the recordings tab of a classical composer at first glance it appears to show all the recordings of the composer when in fact it really just shows the recordings that have not been entered according to the CSG. Although as stated previously I would prefer if classical recording artist did include composer my main concern is to have a UI that aid a consistent way of adding data whatever that way is.
Changing everything to [unknown] now makes it much harder to assign the stuff properly in the future, not easier, since the recordings are harder to find that way if someone wants to clean them up properly, especially if they havenāt been linked to works yet. At least now you can easily see which ones still need attention for a specific composer and work on that (in [unknown] theyād all be mixed up).