Even better, I kept a backup of the database.
Before deleting the 6 shelves using the Glo's UI, the table had:
Code:
CreationDate Id InternalName LastModified Name Type _IsDeleted _IsVisible _IsSynced
2012-11-09T20:35:21Z Asimov's 2012 Asimov's 2012 2012-11-29T09:51:31Z Asimov's 2012 true true false
2012-11-09T20:35:24Z Hervey Hervey 2012-11-29T09:51:36Z Hervey true true false
2012-11-09T20:35:27Z Oscar Wilde Oscar Wilde 2012-11-29T09:51:42Z Oscar Wilde true true false
2012-11-10T10:32:47Z c028e3df-7dc6-4611-863e-cf951ada3be2 Hervey 2012-11-29T09:51:36Z Hervey Custom true true true
2012-11-10T10:32:47Z 7cae2e8e-7f28-47ff-95ed-420dcecc91a2 Oscar Wilde 2012-11-29T09:51:42Z Oscar Wilde Custom true true true
2012-11-10T10:32:47Z 04f55bb0-ad90-4cda-97e7-8db8ca458f92 Asimov's 2012 2012-11-29T09:51:31Z Asimov's 2012 Custom true true true
I only had to actually delete 3 shelves, because the duplicates disappeared by themselves when I deleted the first shelf in that pair.
As far as I can recall, after I deleted all the shelves via the Glo's UI, I was still left with the 3 records where Type = 'Custom', but no shelves showed in the Glo's UI.