What is the Shar'i ruling on how to pay zakat on additional funds accumulated over years, and is what the questioner did by delaying the zakat on new funds Islamically permissible?

There is no blame upon you for what you did, whether it was to hasten the Zakat for the new money, or to pay it when a year has passed over it. This is because if the money acquired during the year is not a profit from the Nisab, its owner has the choice between paying its Zakat along with the Zakat of the Nisab upon which a year has passed (which is a permissible hastening), or to designate a separate year for it and pay its Zakat after a year has passed since it came into his possession, and he pays its Zakat by adding it to the first Nisab.