I should imagine his achievement is several multiples more than anyone else could match, even if one includes all a/c.
The late Darrol Stinton once told me that he'd stopped counting at 150, in the middle of his civilian test flying career. I doubt that Darrol was close to Eric's record - but think that he was probably over halfway.
I can't offhand think of anybody else likely to have come close - maybe some of the old guard ex-military FAA Test Pilots like James Plackis?
G