How is the Graphic Raptar different to otherwise similar enlarging Raptars?

I have a Wollensak Graphic Raptar 3" (74mm) F4.5 which is quite a nice lens, no complaints, but I don't know anything about them or their intended application.

What's special or different about the 'Graphic' versions of Wollensak lenses? Any resources or references that I can look at to find out?