@2manydogs - There are situations where companies do not have to return the excess such as two different companies. The IRS publication 525 addresses this situation when the excess is not returned by April 15. It must still be reported as taxable wages in the year that the excess contribution was make, but can remain in the plan and earn earnings until eventually withdrawn at retirement, however, it will be just like all the other before-tax money in the plan so will be taxable income when distributed.
For information see IRS Pub 525 page 10
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-pdf/p525.pdf">https://www.irs.gov/pub/irs-pdf/p525.pdf</a>
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
