If the 2020 From1099-R was intended to report tax withholding, it would have code 7 (assuming that it's not an RMD from an inherited IRA, in which case it would have code 4), would be reportable and taxable on your 2020 tax return and any tax withholding would be credited on your 2020 tax return. It would have nothing to do with your 2019 tax return. If all they did in 2019 was fail to withhold from the gross amount of the 2019 distribution some amount for taxes, there was really nothing they could do in 2020 t correct that, so it's not clear what they were trying to do with a distribution in 2020.
