Well by definition tge knot is end grain, so at the very least it needs to be sealed it would just suck up finish like a straw.
I'm sure he had noissues turning that butt, at the same time I doubt he took that knot for granted,especially when cutting in the points.
There had been a few acoustic guitar builders who used knotty woodto prove it not the woid, but the maker...
Sealing is standard so as I said at least THAT was done. If I were to ever use any wood with knots I might use some CA or thin epoxy and hope it seeps in.. But I wouldn't make it a practice to use wood with knots for cues.
Being a musician, I haven't seen many if any guitars that I can recall with knots in them especially acoustics. That could be a disaster waiting to happen... I'm sure I prabably have just must "knot" have thought it was a big deal.:wink: