HSA amount in W2 box 12 code W doesn't match 5498-SA amount

[WST2]

My son's school employer added his contributions from his 1/8/2024 paycheck to his W2 Box12-CodeW for the 2023 year. However, the HSA custodian has the online 5498-SA only including the employer contributions through his Dec 2023 paycheck (early December). The difference between box 2 of the 5498-SA (box 3 = 0) and the W2 box12 is the January 2024 paycheck amounts, and he didn't make any contributions outside of these.
Who is wrong, the custodian or the employer? Is this something that needs to be fixed? He isn't anywhere near the max limit, so that doesn't come into play, it is only about $670 on the W2 and $320 on the 5498-SA

[Mike9241]

If a participant designates contributions made at the beginning of the current year to be counted in the previous tax year, those contributions should also be included in Box 1 of Form 5498-SA

[WST2]

He didn't. The extra amount is the company contributions to the HSA. But they were on the 1/8/24 paycheck. The company/school added them to the W2. It was perhaps subtracted from the salary for the year, but we didn't look at that.

[WST2]

The HSA custodian said that since they didn't receive the December paycheck's HSA contributions until 1/8/2024, they aren't part of the 2023 contributions. The school took them out of the salary for that month and so put them on the December paycheck and so they were included on the W2 in 2023.

I suspect the custodian is correct, but I'm not really sure.

[dmertz]

Both are correct.  The total amount of contributions made for 2023 under these circumstances cannot be determined from just the 2023 Form 5498-SA because the 2023 Form 5498-SA has no way to show contributions made in 2024 for 2023.  That information will be reported on the 2024 Form 5498-SA which will not be available until next year.  When preparing the tax return, ignore the 2023 Form 5498-SA.  Enter the  amounts shown in box 12 of the Form W-2 in box 12 of TurboTax's W-2 form without modification and nowhere else in TurboTax.