I think it's just that the material itself shouldn't be in your ears for more than 30 days, not necessarily the same pair of plugs. So unless you're stretching fairly quickly and getting a pair of plugs in a safe material when you get to the actual sizes, they're going to be in your ears for way longer than 30 days.
Also, I think anyone using these should stop at each size for several weeks rather than stretching continuously every 10-30 days. Snap Plugs are kind of like the taping method, but not quite as gradual.
I have 1/2" lobes and 11 piercings: left helix x2, both conches, both nostrils, septum, navel, and VCH.
My lobes are small but I know a lot about stretching and how to do it safely, so message me if you have any questions!