I also maintain an excel sheet to track payments of my 20+ cards.
For added security I have used colour codings…like 1 day before the due date, that card’s row changes to yellow colour….on the due date it becomes green…and after due date it’s red !!!
Also, I’ve incorporated formulas for credit limit utilisation, annual spends tracking to meet spends criteria for fee waiver for paid cards, etc. !!
Took lot of time & research…but made card management stress free !!