In Artwork view only artwork associated with the first track is shown when 'enable all artwork to be selected and displayed' is checked
If extra/different artwok is available eg. for a second disc, it isn't shown even if the subfolder it resides in is specifically selected in the Artwork Retrieval Filter.
Since that hasn't been changed (I made a wish about having that altered a long time ago) I decided that having the PDF icon from the Track Information panel also show in the Artwork panel might be an easier wish to be granted