They opened the can under orders from Vulpes Inculta without knowing what was inside. Hence the pile of Legion corpses in the firehouse garage.

In my hunt for the unique Fire-Axe Knock Knock i stumbled across a large number of logs and other assorted story goodies but couldn't find anything in reference to dates and/or time in them. Also Im curious as to how some of the troopers went entirely feral while other ones apparently can wield knives but for whatever reason still attack you.

Camp Searchlight looked to be a pretty good stronghold for the NCR for a time. However, their supplies were getting robbed by the Legion via Nipton. You also find out the patrols around Searchlight were not very good, and there were plenty of holes. The Legion exploited that by sneaking some soldiers in and having them open up the cannisters of radioactive waste (of some sort). One of the logs mentions that there was a truck or two of waste in the firehouse, and another was routed to Cottonwood Cove (you have the ability to open the cannisters onto the cove, actually). One of the ghouls (pvt Edwards) mentions that everybody became ghoulified thanks to the 'radiation bomb' or something. He must have been protected enough not to become feral, I suppose.

As for the Return of the Living Dead reference, perhaps, but there is a better one at the Old Nuclear Test Site, where you find "Trash" and her die-ary entries. IIRC, Trash was the crazy goth chick obsessed with death in the RoLD movie.