The land of the Suvidehans is only mentioned in MN 34, where it is adjacent to Magadha, on the far side of the Ganges. Ven Bodhi follows Nyanamoli in rendering it as Videha, without comment. Ven Nyanatusita, commenting on this (private document) suggests that the prefix su- is meant to indicate that the far shore, as in “among the good Videhans”. The commentary merely uses Videha without comment. The Dictionary of Proper Names says that Videha bordred the Ganges (and, improbably, Kasi and Kosala).
I don’t find any of this particularly persuasive. It is well established that the capital of the Videhans is Mithila, to the far north in modern day Nepal. And it is also well established that the Vajjians bordered Magadha on the Ganges. Unless we are to assume a long, thin, north-south orientation (think Indian Chile) it seems unlikely that Videha bordered the Ganges. I can’t find any other sources that support this. If it did, however, we would need to redraw our map.
Videha appears as a kingdom frequently in the Jatakas, and it appears that, along with Benares, it was one of the older centers of Vedic culture, which was being eclipsed in the Buddha’s day by the more economically dynamic centers of Sāvatthī and Magadha. This being so, it would not be unlikely that as the nation contracted, groups of people identifying themselves as Videhans would be staying outside the main region. Note that Suvideha is never identified as a political entity, the text simply uses the common idiom “among the Suvidehans”.
Given the lack of corroboration, it is probably best to simply translate the passage in MN 34 as is, and not assume that the maps need to be redrawn.