Hey there -
yes, it's improper to use the term 'tharbad' to imply 'city of Tharbad' or 'city of Tharbad held by Dunedain', for the pre-Rohan history and also for the Numenorean presence pre-Third Age. Tharbad was a Numenorean stronghold, I just re-read. Joining Arnor and Gondor and the Greenway over the bridges of Tharbad. A region apparently drained by the Realms in Exile and a city plonked on stone above fens.
The Dunlendings, though I also just read were descended from the House of Haleth and were "distant" relatives of the Numenoreans. Described as tall and dark haired and jealous of Numenoreans. Enemies of Rohan. They occupied the lands surrounding and Numenor felled significant trees from the region.
I revise the entry I wrote to read:
Sauron sent forces that were coming in front the South East and were in Enedwaith
--at the crossing of Tharbad--
(at the time, that was prior to Numenorean engineering the causeway at Tharbad. I'm pretty sure there was no 'city of Tharbad' at this time, because it was mostly water and fens). At the time of the War of Elves and Sauron, that was only lightly held by Sauron. I re-read though that the gist of it all was that the Dunlendings were rather hoping Sauron would oust the Numenoreans from the region. I'm not sure if Dunlendings actually fought for Sauron. I need to brief myself on this last item