CDS should keep a list of files it was unable to index, so the user can seek to solve the problems with them. As it is, CDS will try futilely to index these files every time the index is updated.
The list should include the full pathname.
A good way to access the list would be a new menu item: Tools > Unindexable files
I agree. The list mentioned by the OP should exist to prevent CDS from trying to index again unless the file has been modified. The list should also be printable or exportable in a human-readable format.
Anyway to see which files / emails were not index, so as to remove or update them would be great.