Excess Deferrals - taxable in prior year, but 1099-R for which year

Excess deferrals due to 402(g) limit are paid out by 4/15.

Question is the 1099-R with Code P generated for the prior year in which it is taxable, or for the current year it is distributed, even though it is taxable in prior year?

If you have an excess deferral in 2020 and issue the corrective refund after December 31, 2020 but prior to April 15, 2021 you would issue a 2021 Form 1099-R in January of 2022 with code P, indicating that the it is taxable income in 2020.

So the participant does not actually receive a 1099-R until long after taxes have been filed. They just provide the information to the tax preparer?

Does the IRS ever end up flagging such tax returns because the taxable amounts don't match what has been provided?

We send a letter along with the refund expaining the tax implications, but yes that's the way the 1099-Rs work.