It's quite possible that a tipping point wouldn't even be recognized until decades after it had passed. In the case of the AMOC, a tipping point would be if the heat already in the ocean and atmosphere is irreversibly going to melt enough ice to stop the current. Given the complexity of the thing, it's very challenging to know if we're there or not.

The "many tipping points have come and gone" claim is just standard climate change denier-speak meant to be dismissive and shut down discussion. |t isn't ever backed up with facts. We may have blasted through a dozen tipping points to hothouse earth already and not even know it. Or not.