Could the various MediaInfo date fields be incorporated into the drop-down list in the AutoDate section?
<($MediaInfo:Encoded_Date)>
<($MediaInfo:File_Created_Date)>
<($MediaInfo:File_Created_Date_Local)>
<($MediaInfo:File_Modified_Date)>
<($MediaInfo:File_Modified_Date_Local) - >
<($MediaInfo:Tagged_Date)>