It has always been JS-LIST, and those who pronounced it "Jay-list" were wrong or just lazy. I recieved my first JS-LIST gear in December of 2002, and a crapload of training to go with it. Our (then) NBC NCO beat the correct acronym into our heads as well.
Even with the short shelf life after opening, we were told in early to mid March, 2003 (by MG Marks, then CFLCC C-2 CG) to pull them out, try them on, and fit the suspenders properly. I think that was our official notification that we were about to go hot in Iraq. Fun fun.
Of course, this was in an intel unit that had been in Kuwait since August 2002, so all the stories of "We're going to Iraq, be prepared" eventually became a commonality and were easily dismissed. Wasn't reinforced until the State of the Union address, when Pres. Bush spoke about Iraq and the evils of Saddam Hussein for a good 30 minutes. Yay.
And while all the tip of the spear guys (whom I've never envied, but am eternally thankful for what they do) were headed into Iraq, for about 37 days, Saddam was shooting his entire missile arsenal at Kuwait (probably because that's where the intel guys were, or maybe he had a specific target and just wasn't accurate). 37 days of continuous MOPP2 minimum, MOPP4 about once every hour or two until the all clear. So in between keeping an accurate portrayal of the battlefield and trying to determine the intentions of the Iraqi military, civilians, cabinet, etc. to brief the CG, we (initially) stopped every time the alarms went off, ran to the bunkers, did a head count, determined if anyone was missing, waited for the all clear, then went back to work.
I said all that to say I'm not overly fond of the JS-LIST, although I do have a rudimentary working knowledge of it.