Can MIP Charges be Filed Months Later, With No BAC Test Results

The police were called to a home due to a 911 call about a possible crime. They found some minors at the home, and the minors admitted to drinking alcohol, but were not tested. The incident report relates only to the alleged crime, and does not mention alcohol or MIP. Three months later the police are threatening the minors with MIP charges. Could charges still be filed?

Yes, charges could still be filed despite a three month delay, and the officers' observations along with the confessions could potentially support a conviction.

I suspect that this may have to do with the alleged crime. Perhaps the police are trying to add an incentive for the minors to be more helpful in relation to that investigation?