Basically, the quote you included form IRS Publication 525 is stating that if your excess 401(k) contribution is not taken out by the due date of your return, you will end up being taxed twice on the amount because they are not allowing you any type of basis when you are taxed the first time. So you are taxed on the excess contribution now AND when you take the money out in the future.
I would highly recommend talking to the plan administrators again and explaining the situation so that you can withdraw that money before April 17, 2018 and avoid the double taxation.
If you are able to withdraw the excess contribution in time, you can report the excess contribution on line 7 of your 2017 Tax Return without a Form 1099-R by following these steps:
- Click on the "Federal Taxes" Tab
- Click on the "Wages & Income" Tab
- Click on "I'll choose what I work on"
- Scroll down to "Less Common Income"
- Select "Miscellaneous Income" and click Start or Update
- Select "Other income not already reported on a Form W-2 or Form 1099" and click on Start
- Answer the Question "Did you receive any other wages? Yes
- Click through the questions until you get to "Any Other Earned Income"
- Answer Yes to "Did you earn any other wages?
- Indicate "Other" as Source of Other Earned Income and click Continue
- For the description enter "2017 Excess 401K Deferrals" and click on Done
