You either got a statement credit, or a bunch of MR points. Go back and look at your previous statements, short of keeping notes, that's all I can suggest. If you took an MR point retention offer it's probably easier to scroll back through the Points Summary activity screen and look for a batch of points with retention in the description. I suppose you could call Amex and ask them, but if trying not to overplay your hand, I wouldn't recommend calling and asking when is the last time I got this offer so I can ask you for it again?

So...you probably had 13 months in between? There's no harm in saying, it never hurts to ask, but I have yet to see a successful data point getting around the 13 month rule even during covid.