Barry,
Whilst the DVD set "Four years of thunder" DOES have flaws and omissions, it is (in my humble opinion) the best work on WW1 aviation available.
There are many "box sets" on the Great War that go into detail on the politics and alliances that sparked the conflict, detail on the ground war and how the front lines moved around, but just barely touch on
the Great War in the air, and the scant information they supply is an overview, not going into great detail as we would like.
"Four years of Thunder" provides the information in brief detail (as is necessary in only 3 DVD's - you can't go into every detail), original footage, mission types, bombers and fighters, aircraft performance etc etc etc.
I think as with most US made documentary series, they concentrate on US involvement.
You won't see better for some time I don't think.