1099R from OPM - includes retroactive payment of 2 pensions

I retired in 2021 and received interim payments on my CSRS annuity to 12-31-21. No problem with 1099R last year. There was a taxable amount in box 2a of1099R. Now it's time to do 2022 the 1099R says UNKNOWN. I just left it blank in TurboTax and it calculated it correctly. Here's the tricky part. I have a second annuity called "Voluntary Contributions" with OPM and it shows the amount on the bottom left of the same1099R for 2022. It didn't in 2021 so I assume there was no payment then since they were still calculating my final annuity. Those familiar with "Voluntary Contributions" annuity know the taxes were paid previously. On January 1, 2022 I received all of my retroactive balances from the annuities for 2021 (4 months worth). When I enter the information using the "Simplified Method" Turbo Tax asks how many months it was this for? I put 16 because that's how many months I way paid for in 2022 (12 months in 2022 + 4 months for 2021 paid retroactively). It's a no-go for TurboTax. It will only let me do 12 months which means I get to pay a few hundred extra bucks in taxes. Any ideas are appreciated if there's a way around this.