This sounds like a very interesting project. I can't go through the entire thread right now, but I sure will sometime tomorrow.
I understand a bit of Neural Networks and comic book grading, so jotting down my initial thought.
I would break the problem in two stages.
First I would start with something simple.
There are nuances that affect comic book grades. Conditions like mold, foxing, stains, staple rust, staple pop, centerfold detached, water damage, subscription crease, residue -- these affect the grade.
I would train a simple feed-forward neural network trained on one hot vector of features, where a feature is a condition being present or absent (mold, foxing, stains, staple rust, staple pop, centerfold detached, water damage, subscription crease, residue), which we would extract from grader notes (text data).
Although this is a very primitive design, this simple setup would be able to make some decent predictions.
Imagine how different features in your one hot vector help train the simple classifier:
Is cover missing? Yes or No. If Yes, then grade is always 0.3
Pages missing? Centerfold missing? Yes or No. If Yes, then most likely a 0.5
Subscription crease? Book length crease? Yes or No. If Yes, then grade most likely in range ~4.0
Once I get this primitive design to work with a reasonable accuracy, then I would attempt the bigger problem.
Trying to design a CNN that takes image data as input to predict the comic book grade, with the one hot vector of features being the intermediate latent variables.
The accuracy of the network would depend on the amount of data you have. But I think it will be able to predict ranges, like a book being in vicinity of GD, VG, F or VF or so on.
Let us know if you make any progress.