Did u dilute the zerotol? In my opinion the problem with h202 products is they add water to the wound or the h202 is so concentrated that it damages the pumpkin. This strong oxidative damage may keep it from healing well on its own? I the advice of "everything can be cured with a fan." But there may have been some extra nasty germs in those critters mouths.. Bummer!
If 'nothing to lose', next time, cauterizing with a torch or if it's ever shallow again, a 'drag type' cheese slicer followed by a Clorox and water spray, daily, 1-2 Tbsp/Gal H2O. I've not had your experience, but they'd be neat to try. I have used the Clorox detail before on a blossom end or two. eg