Oh Pat, you are a very naughty boy!

As long as the knot is sound I don't bother plugging it. You still need to compensate for it in the bow's layout, especially on the width of the back.
If the knot is loose, I will clean it out, then plug it, with a Dutchman.
I cater the shape of the plug to the shape of the knot. Dowel if possible, otherwise conical taper, with a flattened point. Never drill any deeper than is absolutely necessary.
Use a really good gap filling glue, like a slow setting, rock hard epoxy, or urac etc.