Regarding your comments on why the bores would need to be plugged during boiling, I can shed a little light, but not much. The mention of this in Oscar's process only comes up after the usage of the logwood in the boil bath came into play. I do not know what problem this mixture of logwood and copperas would cause in the bores, but that is where the vented plugs came into use. I don't think he ever plugged them when boiling in plain distilled water. I, like you, have boiled quite a few sets in plain water with no problems, but I have not used logwood as of yet. We do plug the bores for the etchant, though.
I am curious about how you go about coating the bores with shellac. How do you do it without getting some on the outside? Does it survive the many boilings without having to be re-applied between cycles? We have always needed a very light bore-honing after completing a set. Will the shellac eliminate this need? How do you get the shellac out of the bores afterwards? Thanks,