You may be right. I wonder if the angle of 7 was changed when digitized - that seems like a sort here that could help solve the mystery for somebody who knows metal types better than I do.
Because the original design for Janson goes back to Nicholas Kis in 1690, it's at least a plausible choice, from a historic standpoint, because this sample comes from an edition sometime after 1876. Do you know the edition's date?