My heart sank reading this because I did almost the same thing last spring with a graded New Mutants 98 that was my uncle's. It sat in a box for months while I waited on a good mailer, and the day the mailer showed up I tripped on the porch step and the case bounced down three stairs. Mine went from a 9.2 to what a shop guy guessed was a 7.5 once he saw the dinged corner, and he flat out told me pressing and regrading would cost more than the value I lost. Call CGC first, they can sometimes reholder a cracked case without regrading the book, and that is way cheaper than a whole new grade. But if the corner scuff actually touched the paper inside, that 9.0 is gone and you are looking at a 7 or lower. Chasing a dog is the worst way to lose a comic, mine was a squirrel, and I still feel dumb about it a year later.