My W2 incorrectly overstated my employer's HSA contribution by $200. Around $1000 was the actual amount I received from my employer as indicated in my 5498-SA which I just received. On my W2 box 12c it was ~$1200.
I made no contribution myself either through payroll or personally. I also don't have any other tax advantaged health accounts such as FSA, etc.
This employer contribution was not part of a salary reduction plan, and so the only correction is the box 12c and all other numbers (including my gross wage) remains unchanged.
Therefore when I re-entered the correct amount in Turbotax my tax refund amounts (federal and state - MI) were unchanged. Also in my 8889 after I made the correction line 2 is NOT more than line 13 so that also remained unchanged, as my total contribution was only $1000 which is under the contribution limit, so I have no additional amount owed for HSA over-contribution.
I already filed my tax for 2018. In this case assuming I receive my W2-c with only correction to W2c box-12c and it doesn't change my tax refund/owed amounts: would I need to file amended returns?
i wouldn't. the worse that can happen is that the IRS asks for an amended return. however, if the IRS does then also file state. IRS notifies states that amended return was file without explaining what was changed. I guess you could wait to see if you get letter from MI then call an explain to see if you could get out of filing.