altered card stock ????

[ruth_rookie]

Hi guys. So glad I stumbled across this forum. The knowledge here is amazing and I find myself reading it every day on my lunch break, and learn something new every time. My question concerns the '33 Sport Kings Ty Cobb that just came back "Altered Stock" from PSA. What exactly does "altered stock" mean? I notice what looks like an "A" that someone at some point during the past 85 years penciled on the upper right corner of the back (pic below). Then looks like someone tried to erase it. Would this be why PSA returned it without grading it? If so, why wouldn't they grade it and qualify it with "MK"? I definitely would've preferred that to simply sending it back unslabbed. Please review my pics and see if there is evidence of altered stock. Or is that something that only they can see with a certain tool? Thanks so much for your help...it is GREATLY appreciated. By the way, I was pretty happy with the two (of the three I sent) that they did grade (pics also below).