Technically it's against the rules. The bigger question is why would you want to have multiple accounts for yourself? There's no reason to do so. Call Marriott and have them merge them into one account and stick with that moving forward.

I just reread your original post. If you're tracking clients accounts/ have access to them and they're in their name then there's no issue. It's their accounts. If, however, the accounts are in your name for the various clients then that's a bigger issue.

Cheers