Matt Whiting wrote:

I don't have a copy of the medical form in front of me, but my
recollection is that even a diagnosis of an illness must be reported.

That was my understanding as well. the form 8500-9 asks specifically:
"have you ever in your life been diagnosed" then lists a number of
conditions; it doesn't ask whether you have ever suffered from said
conditions -- and chose to sit it out and wait to get better and/or
remained undiagnosed for whatever reasons -- but whether you have
been diagnosed -- wrongly or not.

--Sylvain