Inaccurate performance data for BOB fighters in COD comparing to RL data

[Glider]

Re the statement
The Germans were sinking British tankers at an increasing rate, and all 100 octane fuel was coming in those tankers....but this was increasingly uncertain as Uboot took their toll on the tankers, and, during May and June, until the French capitulation, with 25% of their fighters and some of their bombers running on 100 octane the British consumed 12 000 tons of 100 octane and 42 000 tons of other (87) grades, or 54 000 ton of avgas at total - and there was no tanker running in with 100 octane until August 1940.

If there weren't any tankers coming in can someone explain how the reserves went up, in particular the 49,000 tons in the six weeks between 31st May and 11th July .
I think we can rule out air freight or submarine cargo

Stocks of 100 Octane
30th September 1939 153,000 tons(b)
27th February 1940 220,000 tons(b)
31st May 1940 294,000 tons(a)
11th July 1940 343,000 tons(b)
31st August 1940 404,000 tons(a)
10th October 1940 424,000 tons(c)
30th November 1940 440,000 tons(a)

PS remember these are reserves total inports would have to cover usage as well