If 2022 TurboTax used the lump-sum election method to calculate the taxable amount of your Social Security benefits, TurboTax would have marked the new-for-2022 checkbox on line 6c of Form 1040. The IRS Automatic Under-Reporter system should have taken this into account. (Perhaps the IRS was overlooking a lot of the "LSE" notations next to line 6a for this purpose on Forms 1040 prior to 2022.)
If you mailed a paper tax return the individual transcribing your tax return into the IRS system could have missed the checkbox on line 6c. Your tax return transcript, downloadable from the IRS, would reflect this omission if that's the case. Even if you e-filed, if your tax return was examined for some other reason, the examiner could have overlooked the marking of this checkbox. It's also possible that the IRS has an undisclosed policy of questioning the use of the LSE if it results in an amount being excluded from income greater than some threshold.
