Craig,
Back in the previous ownership days, I submitted several OJs to SGC that were either pretty trashed, skinned or rebacked. I knew the cards were altered or in such bad shape they wouldn't receive numerical grades so I requested them be slabbed a "A" (authentic) and that it would be understood that a numerical grade was not possible for the card. My request included the same reason you mention, preservation. They were good about it and slabbed them with an A grade.
And yet they still provide numerical grades to cards that have had part of the bottom portion of the card removed
