I've cracked. I just shouldn't have left it here by my computer:
I've been thinking. The brush was made in 1919. It got a new knot much later. So the handle must have been well used. The knot is still unused. But I have no particular wish to preserve a new "old" knot. So I've decided I may as well bring the brush into use again - this weekend perhaps. I'll post pics of the brush once it's been in action. Everyone's entitled to change their mind.