I don't have time to thoroughly examine your references right now, but I can tell you off the bat that the third study is very poor - they measured vapor samples at 500°F and 600°F, which is substantially in excess of normal vaping temperatures and would almost certainly produce an acrid, foul-tasting vapor. The presence of CO in the vapor samples clearly indicates oxidation rather than vaporisation. Of course you get lots of nasty byproducts if you burn the liquid.