I had two offers for Nature’s Way Alive! vitamins in my IB gallery... $4/1 and $2/1, both for the same stores. I purchased a 50ct variety from Walmart for $7.98, and the deals stacked within IB, making it $1.98 oop. Not a MM, but it was interesting to learn that deals can stack within the app.
EDIT: Ibotta’s position is that duplicate offers are considered errors; therefore, if they automatically stack, then one should be removed during the redemption process.
Yes, deals can stack even within ibotta. Sometimes an ANY BRAND offer stacks with an item that I'd never consider would be a match. That's one reason why I like to scan items (even when I know they match the main offer) because sometimes they surprise me with a stacker!