I might have found a Bug: I was replaying the start of TSG5, sent the Jag on a bee-line to El Dorado (since I knew where it was ) and got the 500 gold bonus for finding it first. Shortly thereafter, I encounter a Chinese Unit, and in the trade negotiations window, I can sign a Research Agreement with China (which I did), even though I didn't have Philosophy, and I doubt China had it that early in the game! Unless that is another bonus from finding El Dorado first, I think it must be a Bug in the latest patch (ver. 184.108.40.206). EDIT: not a bug after all, I was misled by the Civilopedia. Thanks to EndoConvert to clarifying this for me!