This is down to personal choice as to what record keeping you attach to your processed films. You can write it in a notebook, a file on your computer or as I do along the top of the film sheet. What data should you record:
1. Date it was developed.
2. Make and type of film.
3. Reference number of the film for your files. I use format size and date of development as a reference number.
4. Developer used.
6. Development time.
The more comprehensive your records are the more you will use it, to refine the processing of your film. Ansel Adams believed in keeping meticulous records, this maybe part of the reason his pictures are so well printed.