That's a beautiful knife! The handle wood is really pretty. Sorry I have not looked up the cocobolo references for you.
I bought a seven inch English scalper from Mr. Willyard several years ago. I sent him a piece of Mexican Pernambuco to use for the handle, which turned out well. He does beautiful work. He is not afraid to make the knife authentically. On those old scalpers, the tang was typically not as wide as the handle, which left a gap or empty space within the tang slot on the underside of the handle. I understand this was sometimes filled with "cutler's cement" (rosin and brick dust), and sometimes not. To the modern eye, it looks unfinished if it isn't filled, but it is an authentic feature and it really makes no difference in the function of the knife. It looks as if yours has that unfilled slot, too, in the old-time style.
Notchy Bob