Limitation Year For DB/DC Combo

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Employer's DB plan has a 10/31 YE whose limitation year is defined as the calendar year that ends within the plan year. Because the plan is fully funded and no contribution can be made, they are considering adding a DC plan so that something can be contributed. Assumedly, the new plan would also have a 10/31 YE.

If the limitation year in the new DC plan is defined the same way as the DB's, it appears that there wouldn't be a problem if only profit sharing contributions were made. However, if they opt for a 401k plan, wouldn't the deferrals have to come out of the compensation that was paid only during the two month overlap between the PY and the limitation year? If this is true, defining the limitation year the same as the plan year would seem more practical, but I was wondering if there was anything in the law that prevents an employer from having two plans with different limitation years. I know this would be difficult to keep track of, and I can't say I'm sure how their CPA would take deductions if contributions to both plans would be allowed some time in the future, but we're trying to find the simplest way for them to make contributions while their DB plan is fully funded. All help is greatly appreciated.