SGC Authentic Altered Jackie Robinson 1954 Question

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First time poster here and looking for some information on my first grading experience. Quick back story, about 8 years ago I bought a 1954 topps Jackie Robinson along with another handful of 1954 cards (Ed Mathews was another one) at an estate sale for $110. I know I got a good deal, but didn't care about the value as I bought the cards for my son as a future gift.

Fast forward to 2025 and my son just turned 16 and I surprised him with the cards. After some research I chose SGC and we sent off the Jackie Robinson. It came back as "Authentic Altered" and we are disappointed. But since it is a sentimental card not about the value it is not a big deal.

If you made it this far I would be interested to hear opinions on the "Altered" part (see attached photos). After comparing to my other cards and examples online it appears the back was either aggressively cleaned at some point or possibly sun faded. Any experts out there that could chime in?? Thanks!