A qarīna is a clue from wording or context that identifies the subject and object. It may be a case ending, a meaningful semantic distinction, or another clear sign.
Labis (اللَّبْس) is ambiguity: more than one plausible reading remains.
In “ضَرَبَ مُوسَىٰ عِيسَىٰ,” absent a further clarifying context, both syntactic roles depend on the indicated word order.