Despite the wording in the announcement, it's not just how you entered. I thought I might be able to get an extension since I entered as visa exempt. But I was told by immigration at Chiang Mai and Lampang, a friend who used to work at Chaeng Wattana, and a couple of agents: if you have held a Non-B since you have entered you will not be granted an extension. Might be different with the Non-O and obviously different offices enforce the rules differently.