Distributions from nongovernmental 457(b) plans are reported on Form W-2, not From 1099-R. Perhaps the employer corrected your 2023 W-2 to reflect that the excess was returned or it was added to your 2024 W-2 (or both, with the excess reflected on a corrected 2023 W-2 and the attributable earnings on your 2024 W-2).
From https://www.irs.gov/retirement-plans/issue-snapshot-457b-plans-correction-of-excess-deferrals
In a 457(b) tax exempt plan, the excess deferrals are taxable in the year of deferral and must be distributed prior to April 15th of the following year. Only the earnings on the excess deferrals are subject to income tax in the year of distribution, and such earnings should be reported on Form W-2 for the year of distribution. If an eligible plan becomes an ineligible plan under IRC Section 457(f) because excess deferrals aren't timely distributed, benefits become taxable in accordance with Reg. Section 1.457-11.
See Notice 2003–20, 2003–19 I.R.B. 894, for information regarding the withholding and reporting requirements applicable to eligible plans in general.
