I am prone to making changes to almost every pattern I use. In order to keep track of my changes, I make a copy for myself to use and I write "working copy" on it to note any changes I make. I do not write in books or on original patterns, but I do want a record of changes I have made in case I desire to make the pattern again. My working copies are kept in a separate file. I never loan my patterns to anyone and if I want to make the same project, I always purchase my own pattern.