I've sorted through thousands of pennies. I do not recall seeing a light mint mark such as this. Most of the D mint marks are so big and fat that there's no question where it was minted at. This one is so faint to the naked eye that it seems like it was punched over to correct a mint error. I tried to take pictures of it.
I don't think I can be of much help, though I not infrequently see parts of dates or MMs even on BU coins.
However, the one you sent photos of is kind of interesting in that the first photo seems like just a 'weak D' mm. But the second large photo almost appears as though there is an 'S' in there ... do you think you could get a really sharp, clear closeup of just the date and MM?
Since I hand sort, hand search all of the coins I get, I frequently see lighter than normal mint marks and mint mark in slightly different places in the earlier years due to how the mint mark was placed on those working dyes.
I believe that during the mid 1990s, the mint mark process was changed somewhat and that resulted in quite a few phantom mint mark errors.
None of my books indicated an error of one mint mark over another for the year of your coin, but to me, anything could be possible. Could you get a clear close up of the mint mark?
If you have a respected coin dealer nearby that likes pennies, take it by there to see what they think.