Zosimus and his sources

[Colonel Chabert]

It is generally accepted that the principle source for Zosimus' Historia Nova in its coverage of the 4th century is the Universal History of Eunapius. This doesn't seem to have provided him with much in the way of detail; both Argentorate and Adrianople are dealt with in a couple of lines, the only specific piece of information about the former being a ludicrously exaggerated figure for German losses. Given that Ammianus had already written his account, partly first hand, of the years 353-378, why did Zosimus not make use of this? The only reason I can think of is that he did not have access to Ammianus' history or was unaware of it. Is this the general belief? It seems surprising to say the least. Would there not have been copies of Ammianus in Constantinople in Zosimus' time? My impression was that libraries, both public and private, were quite numerous in the major cities of the Empire and, even allowing for the damage sustained by the Imperial Library in a fire a few decades before Zosimus wrote, I would have thought that there would be other copies of his work in Constantinople. 

Your thoughts/information on this would be most appreciated!

Cordialement

Le Colonel