+1, I've used an 8s lever with a 7s setup for years with no issues. However 6s and 7s are different spacing, unless the 6s is what used to be called "ultra 6" or similar, namely a 6s cluster spaced the same as 7s to work with 120mm hubs. (I don't know if they did this with wider hubs).
Take quick measurement of the cassette overall width or the sprocket to sprocket spacing and the mystery will resolve.
In any case if it works, you shouldn't care about the extra click. With a bit of creativity, you might use it to advantage by making a chain hanger and using it to shift onto it for wheel removal a la the short lived Campagnolo system.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.