Difference in CFM: Carter & EdelBrock

[GSDrew]

I've decided to upgrade to a Carter Competition series 9625, rated at 625 CFM, to feed my warmed-over (headers and Isky cam) 340... mainly because it was free. While doing some background I've found that the equivelent Edelbrock (1406), has the same size Venturies (1 & 3/16" P. and 1 & 9/16" S.) and Bore diameter (1 & 7/16" P. and 1 & 11/16" S) but it's only rated at only 600 CFM. Anyone know why the Edelbrock is rated lower?
Thanks,

[Buford]

Apparently it was a move by the Carter "marketing boys" before Edelbrock entered the picture, as the same carburetor without the electric choke is rated at 600 cfm. Let's hear some other opinions.:-) Frank