Gospel of the Hebrews (Egypt, mid 2nd century CE) All that survives to us from the 'Gospel of the Hebrews' are several quotations made by Clement, Origen, Jerome, and Cyril of Jerusalem. Jerome took a lively interest in this book, an Aramaic copy of which he found in the famous library at Caesarea in Palestine. More than once he tells us (and with great pride) that he made translations of it into Greek and Latin. Unfortunately, these translations have been lost.
Maybe that was written before something else was discovered? I really don't know, since I haven't read it yet! :o)
A lot of those early works are only found in the writings of their "orthodox" opponents. And yet on another thread this afternoon I've been arguing with someone who insists that the church never destroyed "heretical" documents. Sigh.