Beautiful piece of work. Lots of detail to look at.

I like that small curl of scroll that drops off of the beginning (bottom) end of the scroll that is cut on each side of the frame in the flat portion just below the bbl ring.

That small, extra curl extends outside of the border line that contains the main scroll itself.
It drops down into the fluted/concave shape part of the frame just below it and that area is otherwise left un-engraved here.

That's a nice way to acknowledge for lack of any other word I can think of that the fluted area is there yet without leaving it plainly and geometrically blank altogether.
Or filling it in with something like a quick cross-hatch or dot pattern . The latter 2 are quite commonly used in concaved surfaces just so there's 'something' there.

Areas left blank can accent an otherwise nearly full engraved piece especially when those plain surfaces are highly polished.
They're on the bbl,,the cylinder, the frame sides and bottom, ect.
Those areas have to be planned for though to make it work when viewed.
He certainly made it work here IMO.