I also had some questions about exactly this yesterday, and just received this e-mail from their customer service:
"Thanks for the email. Any time your lowest sub-grade occurs twice (in this case you have 2 8.5’s) the overall grade becomes that grade. For example, if you have a card that is 9.5, 9, 7, 7 then the overall grade is a 7. If 1 of the 8.5’s were a 9 then the overall grade would have been a 9.