Chorus score is by definition the choruses only, printed without any of the solo passages and without the piano reduction accompaniment you would expect to see in a vocal score. Choirs don't like them because they have to count bars' rest instead of following the accompaniment for a cue of the next entry. However, they can be cost-effectively unavoidable if, say, vocal scores cost ?20.00 and chorus parts ?3.50!
If your library has only 20 copies and you need 100, why can't it enquire about interloan availability for the other 80? You need too to be aware that there are held in library stocks a number of different and incompatible editions with different translations, paginations, versions (eg. "full" or "concert" version).
To see what's held in UK music libraries, look at Encore!, the UK catalogue of sets of performance music in libraries. The web address (suggest you lock it into your favourites!) is:
http://webhotel.mikromarc.no/encore/eng/mi.../main.idc?dbAliRegards,
Roger Taylor