This is just a guess. I was wondering the same thing, but decided that co-depency suggests that there's a symbiotic relationship between the dependent and the non-dependent (like the co dependent relationship implies that they need each other for whatever reason.
But, that dependent personality disorder person is dependent on other people or another person without the other person necessarily needing them. (maybe?).
Maybe there isn't much difference other than co-dependents don't necessarily have a DPP except situationally (maybe in reality they have a differnt problem that makes them dependent) and the other person just wants to take care of them, but that person helping doesn't have a personality disorder unless it is a disorder to have to take care of another person. If it is, I'm not too sure what that disorder is -
*** Wikipedia says co-dependents are like introverted narcissists*****
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