Sometimes people can get frequencies and talkgroups interchanged, they are different as we know.

On the radioreference admin side as I'm an admin, if there are duplicate talkgroups in the same system, it will 'flag' these and we will know.

Frequencies; likely will be duplicated, but you have to take note if they have different PL-DPL's. If they are the same frequencies and PL-DPL's in the same city or county, send a submission to radioreference on the frequency page in question to get it looked into and/or corrected.

In Michigan I have gone through every county in the state and fixed and removed duplicated frequencies I think last year.
They do exist, but likely not in MI. :)