Thank you Zhouyi Zhang! You're a star.
If I'm understanding, the problem is that we need the last year value added in our data set so that we can perform the fixed calculations without them being a table calculation. That way, we can fix the last year value on college by year since price drop, fix the current year value on college by year since price drop, then run the difference, and divide by the last year value.
That makes good sense, and better yet, it really really works. Adding the join with the prior year's data was crucial to solving this problem. Huge thanks!