I agree with you that this "after the fact" approach won't work. What we have to do is be proactive. Type out the argument for why "you" believe that comics qualify for media mail shipping into a Word document, lead off with "Dear Postal Inspector,...". Print this, and place that sheet of text addressed to the inspector right inside the package on top of the comics. Then, when he/she opens the package, hope that he/she rationally considers the argument.
This is what I do when I use Media Mail to ship Mad Magazines (which don't contain ANY ads from any era, by design)...I'm not kidding. Some of you who have bought Mad Magazines from me know I'm not kidding.
Wombat's woeful lack of understanding of just how bureaucracies operate aside, I'm not making the case that anyone would be able to ship comics with expired ads via Media Mail without consequence. Obviously, it's not really a fight worth having if someone at the USPS challenges it, and there's clearly a measure of risk involved because of the lack of clarity in the DMM.
It's simply the reason why it could be done, legitimately, if anyone was worried about the regulatory validity of doing so.
If it did I'm sure a new one would be supplied in short order.
Snide commentary makes this a worse place, for everyone.