Since some of my historical picture books were published as long as eleven years after I researched and wrote them, I found it absolutely essential to keep a running bibliography as I did my research. Also, I photocopied the title and copyright pages, as well as the more important pages within each book that had the info on them that I was using. Those pages got stapled together and put into my research folder. That way, I didn't need to keep the entire book for just a few paragraphs or pages of pertinent information and later, if my facts were challenged in the copyediting phase of publication, I didn't have to search through entire books to find the relevant information.
I did the same thing with info from the internet - copied and pasted the info directly from the websites. And I ONLY use accredited website info - historical archives, original diaries, etc. I am extremely cautious about using info from universities, because if it was posted by a student, you have no way of knowing how accurately - or from where - the students researched their facts!