in order to fix the multiple entry problem there are a few options you could take:
1. instead of adding a given entry have a dialogue option merely switch a (readable/hidden) i/o trigger to possitive. basically all entries are in your book from the start, you just cant read them. with this a per save file and a as it is lived through option would both be easy to do.
2. when you have the go back option have a bit of code search for the entry triggers and remove said entries
3. make a given "add entry" command check for a file by that name first
4. have the encyclopedia check for and remove duplicates wheneveer it is opened up
5. have the game remove the entry summon command after it has been done once
6. have the reverse thing actually not reverse but instead create an identicle scenario that happened after what you already did but that wont trigger one time things again