Time period of 150 octane P-47?

[Voyager]

So I picked up a copy of Battle Over Europe, and I've been tweaking it into Il-2 1946 (It was released for Il-2 FB, and never updated to '46). From Baugher's P-51D/K page, I believe it's reasonable to allow the P-51D-20NA in any spot that the P-51D-5 is available, but I'm having more trouble determining when the P-47D (Late) comes in.

To the best of my understanding, the P-47D (Late), is just the P-47D-27, using 100/150 octane, instead of 100 octane fuel, but I'm having trouble figuring out when that transition started, and ended. I've turned up some interesting bits, such as 115/145 being purple, but 100/150 being a different colour, and on Baugher's site the R-2800-59 is listed once with a power of 2,300hp, and later as being 2,535hp, which seems to match the 100/150 power version having close to 'M' model performance (2800hp), and some allusions on Wikipedia to it becoming available in limited quantities in "late 1944", but that's about it.

Any ideas?

Harry Voyager