i called dexcom, and the customer service representative i talked to named samantha was very pleasant and helpful. they're going to replace the sensors i haven't used out of the crap box i have because she understands the hassle of putting one on, having it calibrate only to peel off. how nice!!
AND, i don't have to return the non-awesome sensors; she said i can still try those and see if they'll stay - although i'm kind of hesitant to do that because it will not be stellar if they fall off again.
but yay for the nice people at dexcom who understand what it's like to work with technology that sometimes doesn't agree with you.
bravo, dexcom! thanks for being my friend. :)