For outgrowing diaper size mid month, we don't see this happen too much, as you start to know when the diapers are getting too small, and can update your subscription. With that said, if you ever end up with a couple of packs of diapers that are too small due to a quick growth spurt, you can reach out to us and support@healthybaby.com for assistance.
Note: Your baby will change diaper sizes faster for sizes 1-3, then will be in diaper size 4 for the longest, before moving to sizes 5 and 6.