I also got the remainder of my February credit today (and it was definitely Feb. as I had already received $30 for March credits before today, and have spent more than $30 via Paypal in March).
I did not contact Amex at all, ever, about these credits. They just worked themselves out.

Interestingly, it was a partial credit for a charge that, if credited at the time, would have been a full credit. So they did the full math on whatever they processed today.

So my pattern was like this:

2/3 - $17.99 charge
2/9 - $20.00 charge
2/11 - $20.00 credit (for 2/9 charge)
2/24 - $5.99 charge
2/28 - $5.99 credit (for 2/24 charge)

3/3 - $17.99 charge
3/5 - $17.99 credit (for 3/3 charge)
3/19 - $22.00 charge
3/22 - $12.01 credit (for 3/19 charge, up to $30 March limit)
3/23 - $4.01 credit (for 2/3 charge, up to $30 Feb limit)