Can you over veg?

Its not really possible to over veg outdoor because the veg cycle is primarly based on the light cycle, longer days during spring and summer keep the plant from going into flowering. THen when fall comes around the days get shorter, less light, the plant knows its going to die and starts to make bud.
I do know that some strains of marijuana have longer flowering periods than others causing the plant never to bud to its full potential because of frost and winter coming, killing the plant early. Some friends I know have grown longer flowering strains, and in order to have them complete their flowering, they have to start flowering during the summer by making sure the plant only gets 12 hours of light a day, puts a garbage bag over the plant for dark periods during the day. hope that helps