Please share with me your banks payment of earnings credit.
I'm trying to see if other institutions "rollover" earnings credit in the event the service fees for the month credit is earned is less than the credit earned. Then the rollover can be used in the event the service fees are higher in a later month. Hope I didn't confuse you.
It's always been my understanding that you can't carry over or apply to other accounts - but may be my understanding comes from my prior employers way of doing business. I have read and re-read Reg Q but find no guidedance.
I think you would be hardpressed to defend yourself from not paying interest on a demand deposit account, if you allowed it to be used toward future charges. Your understanding is the way I have seen it work for the last 25 years.