I think this might get you what you want in query format.
--This gives the archive name and count of items by retention cat.
--Runs against the VaultStore Database
SELECT rc.RetentionCategoryName, ex.MbxDisplayName, count(s.RetentionCategoryIdentity) as 'Number of Items'
FROM Saveset s
Join Archivepoint a on a.ArchivePointIdentity =s.ArchivePointIdentity
Join EnterpriseVaultDirectory.dbo.RetentionCategoryEntry rc on rc.RetentionCategoryIdentity = s.RetentionCategoryIdentity
Join EnterpriseVaultDirectory.dbo.ExchangeMailboxEntry ex on ex.DefaultVaultID = a.ArchivePointID
GROUP BY rc.RetentionCategoryName, ex.MbxDisplayName
--This gives the count of items by retention cat.
--Runs against the VaultStore Database
SELECT rc.RetentionCategoryName, count(s.RetentionCategoryIdentity) as 'Number of Items'
FROM Saveset s
Join Archivepoint a on a.ArchivePointIdentity =s.ArchivePointIdentity
Join EnterpriseVaultDirectory.dbo.RetentionCategoryEntry rc on rc.RetentionCategoryIdentity = s.RetentionCategoryIdentity
Join EnterpriseVaultDirectory.dbo.ExchangeMailboxEntry ex on ex.DefaultVaultID = a.ArchivePointID
GROUP BY rc.RetentionCategoryName