It's interesting that so far ORB was found that mentions the switch to 100 octane fuel after May 1940. Of course some ORBs don't mention the switch at all. However if at least one squadron could be found it would clearly proof that it was not in use by all squadrons.
BTW: Anyone know what Merlin Modification 102 and 123 was? It was applied to the Spitfire of 41 Squadron in November 1939:
http://www.oldrafrecords.com/records/424/4240052.gif
Also I remembered that there are two different Pilot's Notes for the Spitfire II are circulating, one that mentions the use of 100 octane only and another that mentions 100 octane (operational) and 87 octane (non-operational). Wouldn't it be logical that the first issue only contains 100 octane use as the new Spitfire II was only used operational at first, and only later when non-operational units used it the handling of 87 octane is mentioned.