Even though NVMIDARVM appears in 1C5, [NVMI]DIA still seems the best conjecture for supplementing the three widely spaced letters DIA, which make no sense alone. If the spacing of the missing letters more or less matched that of the three preserved (as it should have), then the start of the region name must have been not far after the end of NVMIDARVM. To have overlooked such prominent letters seems remarkable carelessness on a copyist's part.
The "D" bisects route linework (but unobtrusively).