What's this? Looks like PMD to me. Oh! The date? Maybe Die deterioration or machine doubling. Either way, no error of any kind.
Need a photo of the whole obverse of the coin... may be a strike thru with PMD or defective planchet.
1991 was struck on a copper plated zinc planchet. What I see is some kind of old clear tape on the Obverse. The rest is post mint plating issues. Damage to the rim and zinc blisters. The date has die deterioration doubling. Aka worthless doubling. Not a doubled die variety and very common issue on copper plated zinc cents.