The addendum sheets sound quite interesting - I will definitely look into that.
As to PDFs, what you propose would be ideal in many ways, but making corrections to PDFs is tedious, requires expensive software, and only works with unlocked PDFs, which are pretty rare. Then of course there's always the copyright considerations and how to distribute.
A good database program makes it easy to add and edit information and updates to online web pages can be made as frequently as necessary.
I hope people will be satisfied to mark up their own paper copies at home. If PDFs can be parlayed into a satisfactory solution I will leave that to someone else in the community.
Thanks for the addendum suggestion. I do hope people will respond with their own error experiences because they would tend to be the most important and commonly-encountered ones.