As long as they're not white and mushy (might lightly press each one by this point) they should be fine. Some strains just take a while to pop. Some of them, that I've tried, at day 20 in the paper towel, whe I try a light press, it squishes, and white goo come out. That one languished and would have never popped. Nothing can be done about this, and is simply a germ failure.