This was keeping me from focusing on my homework so I had to try something… I went through my Categories sheet and Budget Journal, shifting everything 2 months in the future, so the budget and journal entries for Nov became for Jan, Dec became Feb, etc… Then I looked at my “new” Jan (which was actually my Nov data) and the Savings column was populated properly, including my soon to be famous $55.66 of interest I received in Oct. 
After I changed everything back, I took a peek under the hood of the Savings Budget sheet. I noticed “Selected Start Period” showed “1/1/2020” in AX3. I changed the formula to “=AX4” (which said 11/1/2019) and the Savings started showing values again. Looking closer at the vlookup, I noticed the “Starting Period” under “Dashboard Settings” and set that to Nov 19, and now all is fine, just a simple settings issue. Though I’m curious why that is a setting since I can’t imagine setting it to anything other than my first budget period since doing so would throw off all of my savings amounts.
It looks like this is already implemented? I have noticed that some go away which is fantastic, but I’m having some more weird floating-point issues on some others. Scanning down the AJ and AK columns in the Savings Budget sheet I see multiple entries that have fractions of a cent. Some are crazy small like “-2.7285118608944E-13.” These are keeping the sheet from treating them like zero values for this purpose.
I figured I’d include a few real-world examples of how I end up with these categories that I eventually don’t want anymore. In some cases, it’s simply an extension of how I set up my first budgets which mirror my bank’s own built-in budgeting features. They allow me to create as many little savings envelopes as I want. In a misguided attempt to keep it simple, I mirrored these in Tiller. For example, in my bank’s setup, I have separate envelopes for “Netflix,” “Amazon Prime,” “Disney+,” and “Spotify” and conversely a line in Tiller for each of them as well. But what I really want is to create a new Category called “Subscriptions” or “Streaming,” or maybe even use my existing “Entertainment” and “collapse” all of those onto one. The kicker is that I don’t even subscribe to most of them anymore and never did all at the same time.
In another case, I save every month into a “Travel” budget. But for about a year I was planning on going to Hong Kong last spring (haha) so set up a separate, additional budget specifically for that. Well, I completed my savings goal for that trip but it obviously didn’t happen and probably won’t any time soon. Now I want to “collapse” that Hong Kong savings into my regular Travel savings. I can go back and manually -$/+$ for every month, but that’s a pain and error-prone… and that’s a fairly simple case.
In another case, when Google announced the new Pixel Buds I knew I wanted them. I normally have a “Blow Fund” budget to spend on things like that, but I wanted to save specifically for them so I did what I do: Set up a budget line and stashed a little away each month so that when they went on sale, I’d have the money already saved and ready to spend. Now that that has happened, I have this “Pixel Buds” category that I’ll never use again. I’d be perfectly happy if I could “collapse” it onto my “Blow Fund.”
I’m contemplating starting with a fresh sheet in 2021, but… ugh. I don’t want to. haha