Well, I'm a little fuzzy on how I am mistaken in posting facts and asking questions. But since you've identified the actual liner and manufacturer, I took a look at their web page:
http://www.nationalchimneysupply.com/MFlexLiners.aspx
Our M-Flex liner, available in 316L/316TI Stainless Steel is designed to reline existing chimneys or be used in new construction. Manufactured in the highest grade mill certified alloys. ...
They do make this read a bit unclear. Generally the way these are made is the actual liner is 316Ti and the additional components - cap, banding, clamps, T's etc are 316L - hence the 316L/316Ti designation.
I think this web page sorts it out a little better:
http://www.chimneylinerdirect.com/product/Flex-King-8X30-316ti-006-Insert-Kit/369.html
Stainless Steel Lining Kit. Includes: Cap, Top Plate, Liner, Appliance Connector, and Installation Instructions. This kit is specially designed for fireplace inserts. The liner is made from top of the line 316ti .006 inch thick stainless steel. The components are made from high quality 316L stainless steel.
Obviously, "bait and switch" is not alright. (though if someone wanted to bait me with a $400 paper thin liner and switch me to a $1200 liner 5 times thicker - I might take them up on the offer) Unless one of the dealers on the forum can chime in and definitively prove different, I'm not aware of any actual liners which are 316L AND .006 inches thick. You either get .006" 316Ti or ~.024-.030" 316L or 304L .
All that aside, in my semi-professional metallurgical opinion, the Ti addition is a bit of metallurgical hocus pocus anyway. True it does prevent bad things from happening when the steel gets to high temperature. But why is that needed? Because the steel is so thin to begin with! If you take a propane torch and point it at a knife blade, that thing will be red hot in just a few seconds. Point the same torch at the top of your wood stove and I doubt you'd ever get it to glow at all. More thermal mass helps dissipate the heat and keep the temperature much lower. It's almost as if the manufacturers created an artificial problem by making the liner metal 1/5th the thickness, then came up with a 'premium' alloy to handle the high heat in the thin metal. So now everyone thinks the high heat 'premium' alloy must be the best thing when in fact, it's a cheaper, thinner product. Equal thickness to equal thickness, yes, the Ti is a superior alloy for high heat, but if the only reason it's there is because the product is 1/5 the thickness - any advantage is nullified.
Again, just my .02 - and I'm not trying to support any specific manufacturer by posting these links, discussing their product, etc - or say National is 'right' or 'wrong' in what they've done. I have no vested interest in any mfr discussed here. Simply trying to relay information and clarify the situation. The bottom line as best I know it - if you have a thin .006 inch liner, it is 316Ti.