I don't think that those two are the same. I purchased a size #12, 707 [30 plus years ago] when I could not get a Series 7 in that size.
The 707 is labeled Pure Sable whereas the 7 is labeled Finest Sable. A pamphlet on the Series 7 talks about using Kolinsky, but non of my Series 7 are labeled that way.
Since then I was able to find some Kolinsky brushes from other makers.
What I can say is that while the 707 does come to a fine point, it lacks the same spring of the 7. It is still a fine brush but I can't find literature on it. I believe that is because it was before the internet. I would guess that the Series 707 has been renamed "Professional Watercolour".
Last edited by adamphotoman; 12-28-2018 at 12:03 PM.