The Tell Ahmar is located 20 km from Carchemish, on the left bank, downstream of the Euphrates.
The Til-Barsip identification is due to Hogarth who visited it in 1908. He found fragments of a large Hittite stele and two lions with a cuneiform inscription of Shalmaneser III, which mentions Til-Barsip.
This site was excavated by François Thureau-Dangin from 1929 to 1931. He discovered a city that has gone through the bronze age and iron age, and several steles, confirming the identification of Til-Barsip or Tarbursiba. This town became Kar-Shalmaneser after the conquest of this neo-Assyrian king during the ninth century BC
Indeed, the annals of Shalmaneser III describe several Euphrates crossed precisely at Til-Barsip, then part of a country called "Bit-Adini".
Subsequent to the mention of several Masuwari kings on stelae found on the Tell Ahmar, researchers say that the same site was the Hittite Mazuwati or Masuwari.
However, the place name "Barsip" is mentioned in the text of a statue of Gudea : it was the extraction location of the stone that was used to make the statue. This shows that the place had the same name already at the beginning of the Bronze Age. This is in line with the results of archaeological excavations, dating city birth at the time of the Ubaid culture.
And the mention of kings Masuwari does not mean this was the name of the site. An another stele of unknown origine mentions a king Hamiyatas ushering a new town at Haruha. So Musuwari appears rather to be the name of a country: the one called Musri by the Assyrians.
My notes of veracity :
The Tell Ahmar was the city of Til-Barsip: 4/5