Looks like die deterioration doubling or maybe environmental damage. The mintmarks at this time were hand punched onto the obverse dies. If a worker punched more than once, but the second punch wasn't directly on top of the first, this would cause an RPM (Repunched Mintmark). Now every coin made with that die will show the exact same doubled mintmark. The main reason I don't think yours is an RPM, is because the "second D" is larger than the mintmark. They should be the same size.
Looks like die deterioration to me as well. The coin was struck with a worn out die. Rather common with steel cents. Either way, with the condition of the coin, there is not much value.
https://coins.ha.com/itm/lincoln-ce...560-16030.s?ic4=GalleryView-Thumbnail-071515# Not an expert with these but it seems to be a common issue with die deterioration.
All 3 of your 1943-D steel cents are from a worn die. The true doubled does have the shadow to the left, all of yours have the shadow to the right. It’s because of a worn die or die deterioration Doubling. Look at the entire coin. You can see signs of a tired die elsewhere, like the L in LIBERTY as the L is touching the rim.
i mean how the die deterioration cause the deterioration of a die used for mint marks? they were punched by hand, so i see no correlation to the L and the supposed doubling
Parts on the die wear and that causes movement, just like you see on your coins. Mint marks were hand punched into the die, not every coin. It’s the worn parts of the die that are causing what you are seeing.
I send you the page with all of the photos of the 1943-D RPM and you tell me that doesn't exactly say anything? Good luck with that.