I'm sorry to inform all of you, but those join dates are all correct. I verified with our install no Ni2.se and the dates are identical.
Do note that we had a forumcrash, and the first week or so, the forum was offlimits because we were rebuilding it. So a large quanity of members found out by IRC that they could enter and register, so they all registered on the same day and nearly same time even.