Suprised it's not a well known number.
Porsche have a similar issue with the turbo bodied Supersport. They know the number of models made, but because the M491 was an option, (albeit an expensive 25% tick box) no records of this variant were kept - except to the USA I believe.
As a result, there are varying numbers bandying about.
Check - sounding like one of those nerds I talk to at car meets
You know it makes sense! 
