It's most likely an extrapolation of the small handful of known photos of the tank, photos of other machines in the same unit during the time period, and a touch of SWAG (scientific wild-@$$ guess) from the artist.
It's pretty darned difficult to get wartime walk-around photos of an individual tank, particularly those which focus on the sort of details we modelers obsess over, so SWAG is sort of a standard approach to things.
Most publishers (Osprey, Squadron Signal, etc.) who specialize in unit histories and profiles of various tanks and weapons systems try to be as accurate as possible in what they present, but they essentially work with the same pool of available reference photos as we do. But, they have historians like Steve Zaloga working with them to get things right. Researchers like Steve and David Bryden are very well-versed in the details and minutiae of these machines - they're very valuable resources to the hobbyist.