Do Amex Cards have separate (non-shared)limits?

I had an MRCC , My First Amex, with 50K limit, which I got 3 months ago. I recently got the Platinum Travel with 6.8 L limit and Smart Earn with 4.8L limit.

Other banks have the limits shared in one way or the other. What's up with Amex? Or will they later increase the limits of all card to the max one?