Just to demonstrate that quite apart from the fact that our manuscript exists, and describes the eastern routes and trade, there is nothing to argue that it was impossible such knowledge could have been in the earlier Mediterranean.
This is part of the new geography compiled by a north African, al Idrisi, who lived and worked on the project in the Norman Sicilian court for fifteen years.
In that same court, John of Montecorvino (1247–1328), would later serve as military advisor to Frederick II before being appointed by Frederick, and by the Pope, to travel as ambassador to China.
To do that, John had to become a Franciscan monk, and did. He was successful in relating well to the Chinese, and he lived out the rest of his life, we believe, in the Chinese capital. Presumably he too had no less detailed or accurate geographic information.
Where it came from and how much of it had been in Sicily before Idiri’s time is not known, but Idrisi interviewed and weighed the evidence collected from both written sources and the extraordinary medley of peoples who stopped in to Sicily and – for fifteen full years – assisted with all the practical resources and influence that could be commanded by Roger II.
click on the map to see the whole thing. Map courtesy of wiki article ‘Tabula_Rogeriana‘
Knowledge about the world east of Suez did not begin with da Gama!