Applying Federal short-term rate to late deposits when more than one q

[John A]

If a plan sponsor is 9 months late in depositing 401(k) deferrals, and chooses to use the Federal short-term rate + 3 interest rate option, how is this applied? The Federal short-term rate changes quarterly. Should the changes be taken into account?

For example, say the Federal short-term rate + 3 is 8% in the quarter in which the deferrals should have been deposited, 7% for the next quarter, and 9% for the next quarter. Should the 8%, 9% and 7% rates be used? Or should the 8% rate be used for all 9 months?

Has anyone had experience with the DOL on this issue that involved more than one quarter?