Presuming it was simply a "number stored as text" issue, I tried refreshing the cells. Didn't change those few problem ones towards the bottom.

I selected column A and changed the date format to d-mmm-yyyy. All but that handful changed displayed formats accordingly. I then added a column to the right and typed in some dates. When I (American) attempted to input the dates with the European date order (23/03/2023) it just went in as typed, didn't pick up the formatting I'd applied. When I typed it in in American order (3/23/23) it displayed as "23-Mar-2023." It leads me to believe that the items that aren't looking right are coming from a system that doesn't default to the same date format the rest of the data has. Different separators, perhaps, or an American format?

There is a formula you can use to essentially flip the date and month digits in Excel without using Power Query; it seems to work on those left-justifying figures, but makes the other ones go completely wrong. It's

and you could then paste those values back. But, agreed, if you are dealing with bulk and frequent data, a PowerQuery solution may be best.