If anyone is interested, I spent a couple of days tracking this down. It was much more difficult than I thought.
I found myself at the "scalemates" website and discovered the Lloyd C.V is kit number 48013.
After scrolling and scrolling and using various filters, I discovered the SPAD VII, kit number 48009 is the earliest WW1 kit.
48009 Spad VII
48010 Spad VII (new decals)
48011 Sopwith Tabloid
48012 Sopwith Schneider (new parts)
48013 Lloyd C.V
All the above are "new tool" in 2002 and the earliest I can find as no other WW1, 1/48 scale kits seem to be listed before 2002.
So, it seems to me we have a winner for the first ever "Special Hobby" WW1 kit, the SPAD VII.

So my little GB for the first WW1 kits from the companies we now have admired for years are:
Eduard: SS D.III
Roden: Sopwith 1-1/2 Strutter
Blue Max: Fokker Dr.1
Special Hobby: SPAD VII
If I'm missing a company or kit, please chime in and let me know.