<VV> Why 6000?

[Borrrris]

The details of "last year" Corvair production fascinate me, and I read all I can find on the subject, but I've always wondered, and never seen it discussed, WHY there were exactly 6000 Corvairs produced in '69. That was clearly a planned number; decided upon in advance by somebody at GM for some reason. 
But who and why?
Does anyone here know?
Thanks, 
  Matt from L.I. ('66 Monza Coupe 110/PG)