IRS Rev. Proc 2005-66, http://www.irs.gov/pub/irs-irbs/irb05-37.pdf (dealing with the new staggered remedical amendment cycle), includes subsection 10.07, permitting the use of the parent corporation's EIN/cycle when there is more than one plan in the controlled group.

Can one determine, if there is only one 401(a) plan, that use of the parent's EIN/cycle is not permitted? Have I overlooked something?

I think it is permitted under 10.05. This seems to apply to your situation, where there are multiple entitities but only one plan. So if the parent's EIN is used for the 5500 filing, then the remedial amendment cycle is determined by the last digit of the EIN for that parent corporation, and that corporation only. I don't think 10.07 is the applicable section in this situation, if I'm reading it correctly.

So I'm saying that you cannot make the determination that you can't use the EIN of the parent. Which I think is agreeing with you.

Thanks.
Although verification is still needed, I believe the plan covers only the subsidiary (possibly the parent has no employees). If that is the case, I think 10.05 does not apply since the plan is not currently maintained by multiple members of the controlled group. However, a simple amendment could probaby cover the parent, so that 10.05 does apply.

Agree?

Yes, I agree. Of course, my opinion and a dollar are still only worth a dollar, so caveat emptor!