You should be able to set up auto-enter calculations to enter this data.
You might also be able to use a script trigger where entering a field of the bottom "add" row enters data into those fields.
I think the auto update sounds like a plan - I could script something but perhaps a sledgehammer to crack a nut.
Here's a question regarding auto update.
If I set this up so that it appears as I need it to in the user interface, will the auto update be affected by imports?
The table I'm working on is mainly populated by imports where the year and category details are pre populated on an Excel sheet. Would that info (which is correct at the time of import) be affected by auto update?
Forgive me, I've not had too much experience with the auto update feature !