I will just add this little piece of information.
In C.Douglas' 'The Secret Horse Power Race" pg 343, there is recorded a planned output of C3 fuel peaking at 80% of production in 1945. The USN 145 July 1945 report states that they estimate that 2/3rds of production was C3 by wars end (both figures are unrealistic). C3 needed much more processing than B4, resulting in a loss. To increase fuel, likelihood of fuel arriving to units, and overall logistics in accessing the correct fuels, there was a serious push in 'boosting' (sorry I cant think of a better term) B4 up to C3 quality. Many engine manufactures were producing their newest engines that were designed to run on the B4. Producing only B4 could have saved fuel by not requiring extra refining procedures.
BUT!
'Boosting' B4 up to C3 quality was nothing short of a disaster. The recipe was flawed and engines began to malfunction.
P.s. rather than 2/3rds of fuel being C3 by wars end, I have found that B4 and C3 were roughly equal, at least in April 1945. From reading into CHA T2422, NARA T321 and the ULTRA files in the HW-5 series, by late 1944 it still seems that B4 was the main front line fuel available to units (this is against the planned 65% as can be read in the planned production in 'The Secret Horse Power Race" pg 343).
TL : DR - To increase avgas production, try to stick to B4 as the main frontline fuel to reduce production related losses (this was actually a course of action that took place, but things went sour by the turn of 1944/45)
There are three different measures you need for a complete picture, stocks, consumption and production - and sadly its virtually impossible ( I have spent considerable time and money trying), to get these three IF you want them to include a breakdown by fuel type. This is the case because the fuels were all made from raw ingredients at blending stations
which were not at the fuel refineries. So you cannot see what was made from the refinery outputs (the fuels B4 and C3 were blended monthly to order, and I have
only found a tiny few blending order requests, which of course does not tell you stocks or consumption either).
I have a bit more info if you look at stocks, although the results here are also partial, as they do not necessarily include every storage facility in Germany,
and also, in the case of the 1945 figures the total stocks are very tiny relative to 1943, so the relative levels of B4/C3 from a tiny total stock
size needs to be taken with caution. However the data plotted shows certain trends which are difficult to discount.
Please note again, this is STOCK, which does not necessarily mean consumption, and since that is not
known, it also cannot be used to infer production. However, the C3 fuel did not store well, so
we can guess that it must be a reasonable picture of production in the 3 or 4 months prior.
Later in the war, the German supply situation became such that the fuel did not really
rest in these tanks for much time, it was supplied more or less as it was blended. So
as the war progresses, this graph probably represents consumption & production to
an ever increasing extent.
I also have a "snapshot" of PRODUCTION in 1941 (do not compare directly to graph above which is STOCK),
which suggests that production % of C3 was about 20% at the end of 1941.