again, past PIPer here ... we were told to crate our chapter headings early on so that when we found some info that related to that area we could easily just slip it in under that heading. One girl had a folder divided into each chapter and would print out her info (or whatever) and just slot it into the folder. I just wrote the shorthand version of the related chapter heading onto whatever the research was so i knew where it was.
Also, having chapter headings early on means you can work on different areas at different times, depending on what research you have at hand. It also means that you can instantly get an idea/thought straight where it belongs without just leaving it to the side to be lost forever.
There's no set rule for how to write the PIP. You just write it however feels comfortable for you