yea, even with overcast or rainy weather, the plants still know when its 12/12 sun/no sun. It's the same reason why the 'light of the moon' doesn't affect plants in 12/12 flowering. I'd agree with Rwise that you can try and add extra light to send it back into re-veg. If that doesn't work, make sure you do that from the start next time; good luck!