So here they all are, in all their glory:
I made all of the belly bands by cutting the ribbon to length (about 11" to wrap around my pocketfold). I had a throw-away pocketfold mock-up that I was using as a "template" for the ribbon.
I wrapped each piece of ribbon around the template, and then ironed down the edges to make creases on either side of the pocketfold. Since the ribbon I'm using isn't wired, I found that ironing the edges helped make it better fit the pocketfold. Side note: I put a pillowcase over the ribbon before ironing it. I didn't want to damage it.
Then I attached the two ends of the ribbon together by pulling it tightly and securing it with two glue dots. After that, I used four glue dots to attach the monogram seals. Once complete, I slid the belly band off the end of the template and ironed each fold for like 5-10 more seconds just to make sure the crease was really good.
So with that, it is official: All individual components of the invitations are done. Now all that's left is assembly. The sense of accomplishment (already) is immense. I can only imagine what it'll feel like when I can drop these bad boys in the mail next week.