Thanks again for all the feedback, @aronos & @matta. You have provided food for thought and have helped clarify my thinking.
I agree that we should track discrete contributors to budget errors. We can still roll them up into a total compensation factor, but they should be discretely visible as component parts.
I built up a worksheet where we can game out various budget errors and see if they are compensated for properly. If you want to make a copy and play with it, it is available here.
There are six sheets in the spreadsheet each testing out a potential problem scenario:
- Scenario 1: balanced budget with no uncategorized transactions + balanced transfers. I think this one is pretty straightforward… Expected February result is slightly unfavorable savings due to net negative actuals should yield unfavorable Savings, but no Rollover Adjustment.
- Scenario 2: Not-balanced budget with no uncategorized transactions. Expected February result is artificial savings due to imbalanced budget ($200/period) should be corrected by Rollover Adjustment on same scale.
- Scenario 3: Balanced Budget with uncategorized transaction(s). Expected February result compensates via Rollover Adjustment for uncategorized transaction(s).
- Scenario 4: Balanced budget with no uncategorized transactions and balanced transfers. Expected February result: slightly unfavorable savings due to net negative actuals.
- Scenario 5: Balanced budget with no uncategorized transactions and unbalanced transfers. Expected February Result: transfer unfavorability makes Available lower (less funds to fill envelopes).
- Scenario 6: Balanced budget but not all categories configured for Savings rollovers. Expected February result: Rollover Adjustment must compensate for vanishing Groceries rollover in Feb period.
Did I miss any scenarios we should be accounting for?
Scenario 6 is the biggest headscratcher for me 
. Because Groceries isn’t tracked as “Savings”, this Available amount vanishes in the subsequent period. It is confusing but I believe this means that the true budget is inaccurately deflated in the subsequent period— i.e. the user’s total Savings is -$45 but should really be -$35.
Overall, I think we land at a formula that looks something like this:
Rollover Adjustment = Net Budget - Net Actuals (only categories with Savings enabled) + Net Actuals (all categories)
This formula 
seems to work for uncategorized transactions, partially tracked Savings, and unbalanced Transfers.
Really curious to hear what you think— would 
any additional feedback you have.
Thanks in advance,
Randy
P.S. With this tool & workflow, I’d like to stay away from leverages account balances, @matta. There are timing and category-to-account linking issues that are fussy there. That said, the new Savings & Debt template (that @heather & I demoed in a webinar today) does allow you to assign accounts to categories and confirm that there is enough money available to fund listed virtual savings categories.