Well I think the Mtt facts (the 13 tested planes that are on average below the centre spec line - 10 out of 13 are below = average < centre spec line) are there that support my opinion that for the 109G the type was on average below the centre spec line and there is good chances that this is the case for any type coming from this company hence also for th 109E.

You insist that these 13 are not representative and keep arguing that it should be the centre spec line that should be taken as the mean value for the 109 while there is absolutely NO fact that consolidates this opinion. Please provide us with some data from test flown 109E that reach 500 kph and more but beware we need data from several individual tests with this result to support your view.

PS: The centre spec line has nothing to say except that this is just the middle value between the acceptance bandwidth. We have no clue that Mtt ever attempted in fact to reach 500 kph (that is this is the aimed nominal value they took into account during the design process) and there is NO facts supporting that the average 109E ever achieved this performance.