(Addendum: When I wrote this paragraph, I was under the mistaken impression that "Day of Burning" was published before "Trader Team.")
I said here that I was not sure about the status of the Cynthians. There is no doubt that this species was incorporated into the Technic Civilization that had originated in the Solar System. The only question in my mind was whether they had acquired the hyperdrive from Terrestrials or developed it independently. However, a society whose highest level was arboreal trading routes would not have been able to develop space technology with interstellar capacity. Thus, the Cynthians, like the Ythrians, must have bought spaceships or the technology to build them from human beings, then become independent spacefarers. The Merseians, rightly regarded as dangerous, are not sold faster than light technology. This is on David Falkayn's specific recommendation. Thus, Merseian resentment of mankind has a long time to mature. A time traveler wanting to change Technic History could prevent the Polesotechnic League from learning that Valenderay had gone supernova.
According to the Chronology of Technic Civilization, "Wings of Victory" is set in 2150. In that story, one character is said to have studied Cynthian trade-route cultures in his youth. Thus, might we arbitrarily date the discovery of Ta-chih-chien-pih, O2 Eridani A II, Cynthia to about 2100? One Cynthian culture modernized quickly but others were left behind and later joined Supermetals. A Cynthian freighter regularly calls at the Solar trading post on Suleiman. We see one Cynthian working for van Rijn and another later in the Terran Navy. Cynthians discovered and named Llynathawr, then sold it to the Empire. There is a Cynthian forest village on Daedalus. And I have probably missed a few references.