I think that’s the “Black Star Promo” mentioned near the bottom.
I just checked, and it seem you indeed have all English versions of Scyther mentioned. I checked all my usual resources when I search for other Pokémon being featured in an artwork, as well as all my own cards (mainly the trainers), but none contained any Scythers. The only three that came to mind you’ve already listed yourself…
I do know of one Japanese card featuring Scyther, but it doesn’t have an English print: Violence in the Safari Zone! (Vending Series 3)
So nice job, seems like you’ve got all of them listed as far as I can tell. 
If you ever branch out into Japanese or other languages let me know, then I’ll create a complete list similar to what I did with loads of other Pokémon (when I have the time - still have some others in the pipeline).
Greetz,
Quuador