Gary I talked to my segmented turner friend today and he varified what I thought and what Andy just said. It's wood movement that causes the bumps not glue creep. I did some research for a while and you can find wood movement charts online for all species. Nobody does it but if you buy woods that have the same movement ratios you could feasibly glue up a bowl and not have it move. Of course you would also have to orient the grain the same way on every ring.
I have tried most of the ways to flatten a ring. You have to find what works for you. A disc sander works but there is a learning curve. Same with a thickness sander. I have put rings on the lathe and flattened them carefully by shear scraping. I have also just used sandpaper glued to a flattened board both on the lathe and just on my workbench. Slow but it does work. I have made rings that were only 1/8" thick and the sandpaper on a board was the only way to flatten those. Just keep at it and you will find a way that works for you.