If there is no state K-1 then you pay taxes in PA. if there is a SC K-1, you may have to file in SC as a non-resident to pay taxes on the K-1 income. there are filing thresholds for SC so it may all depend on how much income the K-1 shows. If you do have to pay taxes to SC you still have to report the income for PA and Federal but PA will grant a credit for some or all of the taxes you owe to SC. you have to amend your Federal 1040 and PA returns to report the income since it seems you ignored the K-1 or had already filed the returns. if you owe the taxes on the amended returns you may be billed for late payment penalties and interest. Pay the taxes with the amended returns. if you owe SC pay with the return. they too may bill you for late payment penalties and interest. you can try to request abatement of the penalties if you get billed.
if you were not given a heads-up that a K-1 was coming, you need to talk to the administrator of the estate.
Unless the 2019 K-1 was final you need an estimate for 2020 so you can put that in your returns so you don't get hit with more penalties and interest.
you would have to talk with a lawyer to see if there is legal action you could take against the administrator to recoup any penalties and interest. WARNING. if the amounts are small it may cost you more in legal fees just to consult with a lawyer
