Retirement Earnings Year

My wife retired in 2020, but due to paperwork delays, did not receive any retirement earnings until Feb of this year when she received retroactive payments covering Jan - Dec 2020.  Am I correct that these are considered 2020 earnings and will be reported on our 2020 tax return even though funds were not received until Feb, 2021?.  So far, we have not received a 1099-R.