I noticed that Polmar and Allen (neither of whom is particularly noted for their historical skill, they are primarily naval analysts, albeit quite excellent ones) were listed, which really proves nothing one way or the other. I have little doubt that the documents are genuine (by the way, pencilling in corrections was not uncommon in the days before word processors, but I take your point re: retaliatory vs initiated), but this still demonstrates little. We have LeMay's orders regarding further strategic bombing from July of 1945 (which include NO mention of gas, though they contain almost endless detail regarding further firebombing), The June 5, 1945 AFPAC Staff Study "Preparation for a Decision to Conduct Gas Warfare", which explicitly rejects strategic use of gas (largely for the reasons that I outlined earlier), but which DOES make the case for its tactical use., Stephen MacFarland's "Preparation for What Never Came: Chemical and Biological Warfare in WWII" (Defense Analysis 2 (1986), pg 112) which contains the following quote: "The massive strategic use of gas was not seriously studied, nor proposed by any major leader. The US Army Air Forces, the service most dedicated to strategic warfare was unalterably opposed to the strategic use of gas"
I could go on...
The point here is not whether some empire builders within the military were thinking about the use of gas, no doubt they were. What is clear is that virtually every other bit of documentary evidence (and secondary analysis from serious historians of the period) conclude that the strategic use of gas was simply a non-starter. I have no question that tactical use was considered, and in the event of an invasion, most likely (sigh...). I would also suggest (without any pride in our leaders for considering this) that the use of herbicides against the Japanese rice crop (as well as blights and blasts) was in an advanced stage of planning, and almost certainly would have been used by the time of Operation Coronet. This latter use might qualify as a war crime...
Gas, nope, sorry....