It was in Germany since about 2001/02 []
He's the graph I plotted comparing MPG combined, before and after after remap with data since June 2003 (2003MY STi), remap was done in Mid Feb 2005. I pretty much exlusively use V-Power, there's no more than 2 tanks in a row without V-Power over that time!
I can't explain November! December I took the car back to the UK over Christmas before it was tuned, but not since, so boosted economy due to long Motorway driving. Feb is mostly driving on Snow so economy drops significantly!