Well, a little bit of a duh moment.

I thought about it more, and decided that since old MSRPs were showing up and only new ones weren't being added or updated, it HAD to be a problem in the update_product or collect_info pages.

I made a backup of my update_product and just copied directly the included file from the MSRP contrib and tada!

Even though I went through step by step multiple times on the instructions, there must have been SOME issue on the update_product page.

This was a good thought experiment, because it was the symptoms that diagnosed it 100%.