^^ It's the latter, like a large darkened area, not ink stains. I haven't tried cleaning it yet since I didn't want to end up ruining the leather. What's a good leather cleaner you recommend? The pre-treating spray I used was the Wilson's Leather brand. Is their cleaner good?
Get some LEXOL cleanser. Now. And double-check your storage conditions.
Worst case~ Black spots can be the start of something nasty in the form of MOLD. Make sure your leather is kept dry, wiped well if it gets rained on, and not placed in direct contact with anything remotely damp, ever.
With rainy Fall weather we all have to be aware of this. I don't have to mention no drying by radiators, do I ?
Now the good news. A large darken area on the back is likely dye transfer from clothing, and you'll find lots of help on tPF, but Lexol can fix that.
If the actual color is coming off the bag, you'd have seen RED showing up where the bag rubbed something.