Do all Bitcoin client enforce checkpoints?
The short answer is no, because you can run Bitcoin Core with -nocheckpoints, and different versions may have different checkpoints.

The long answer is that it doesn't matter. If checkpoints ever actually prevent a reorganization of a fully synchronized client, it means that the assumptions on which Bitcoin's security relies (collusion of a majority of hashpower to rewrite the blockchain is too uneconomical to ever be a problem) are fundamentally broken. Checkpoints are not a security feature for this reason, and are often mistaken for one.