Unfortunately, it's full of fairly typical weasel-wording to amp up the impact of Koga's Zero. For example, the "full capabilities" were "largely unknown" which, I'm afraid, is bogus. The full capabilities may not have been entirely appreciated but most key performance measures WERE known and, for example, were circulated to RAF squadrons in the Far East at least as early as November 1941. Whether those warnings were heeded was a separate issue...but that's not something that Koga's aircraft resolved.
To suggest that the Zero's performance was "largely unknown" in the summer of 1942 is massively overstating the situation.