that the indexer has used?
For the most accurate answer, please post the Batch Code - the letters and numbers inside the brackets at the end of the batch name - [XXXX-XXX].
If yours is Muster Rolls and Rosters batch and the date is the Military Date, the Indexer might have looked at a previous (-1 through -5) Reference Image to find the first page of that list, which is OK. Use the last icon in the little vertical toolbar (it looks like an open book) to show or hide the Reference Images. You will often find the date of that whole list/Roll or Roster (including your batch image) at the top of that first page of the Roll or Roster and sometimes on intervening pages. That Roll or Roster date may be used as the Military Date for all soldiers in your batch who do not have their enlistment date shown. If the enlistment date is present for any soldiers, those soldiers get the enlistment date indexed as their Military Date.