Anyone that wants to dispute it, should take it up with the company - Anavex.
Investor2014 has a pretty good explanation for the large number of 7,000. He claims it was fed into the KEM analysis to come up with a simulation comparison of how 2-73 works. (See his comment below)
"No the 7,000 historical RWE AD data is a comparison input into the KEM analysis to illustrate a simulation of how A-73 performs."
And Steady_T further clarifies Investor2014's comment...
"So if I understand what your post is saying the 7000 is the historical tracking outcome of 7000 AD patients used as a basis for comparison with the 2-73 subjects. A historical control group as it were".