Mom, 85, was the ben of dad's, 89, IRA. He died in Sep. The IRA was rolled into mom's IRA in Nov. A mrd was done to dad's orig IRA in Dec. Why does TT show it non-tax?

Mom, 85,  was the beneficiary of dad's, 89, IRA. He died in Sep. The IRA was rolled into mom's IRA in Nov. A mrd was done to dad's orig IRA in Dec. The 1099-R was received in my mother's name. Why does TT show it non-tax?