The Electoral Count Act of 1887 says that the electors who are sent in accordance with the state laws in effect prior to Election Day are the ones who will be accepted. It's up to the two houses of congress to decide which set of electors represent the state in accordance to those state laws. If the two houses of congress can't agree on which set of electors are those are, the set of electors which have the state governors seal of approval will represent the state.