When Orson Hyde was on his way to Palestine to dedicate the land for the returning of the Jews, he stopped in Germany. He wrote a German-language pamphlet Ein Ruf aus der Wüste [A cry out of the wilderness], the earliest church publication in a language other than English. In describing that pamphlet, he wrote,
"I have written a book to publish in the German language, setting forth our doctrine and principles in as clear and concise a manner as I possibly could. After giving the history of the rise of the church, in something the manner that Br. O. Pratt did, I have written a snug little article upon every point of doctrine believed by the saints. I began with the Priesthood, and showed that the saints were not under the necessity of tracing back the dark and bloody stream of papal superstition to find their authority, neither were they compelled to seek for it among the floating and trancient [transient] notions of Protestant reformers; but God has sent his holy angel directly from heaven with this seal and authority, and confered [conferred] it upon men with his own hands: quoting the letter and testimony of O. Cowdery." Times and Seasons, 1 October 1841.
Oliver Cowdery's letters were the first published account of the restoration of the Priesthood, so it's understandable that Hyde used the Cowdery letters. This means he must have taken a copy with him. This was after the republication of those letters in theTimes and Seasons and Gospel Reflector, so maybe he took a copy of one of those with him. (The March 15 Gospel Reflector would have been the easiest, since it contained all the letters in one issue.)
It's also interesting to know that Orson Pratt's pamphlet, A[n] Interesting Account of Several Remarkable Visions, 1840, online here, also contained part of Cowdery's letters (including Letter VII).
This is all just additional evidence of how well accepted Oliver Cowdery's letters were during Joseph Smith's lifetime.