I'm trying to get Days 12-13 out by the end of the month. I can't say with 100% certainty that it will be out by then, but my fingers are crossed and I'm working hard.
I never considered the situation you described with upgrading from the $5 to $20. If you're interested in that we can figure something out.
Each update that comes out will unlock the previous versions on the same tier. If you get the Days 12-13 $20 version, you'll get Days 9-11's $20 version automatically with it.