Failure to Timely Adopt Proposed Amendments Per IRS Determination Letter

[401 Chaos]

I originally posted this on the Plan Correction board but have not received any responses and so thought readers here might have some thoughts / experience on the question below:

What is the usual procedure for correcting a 401(k) plan's failure to timely adopt proposed amendments submitted in connection with application for determination letter on continued plan qualification? Here a Cycle A 401(k) plan restatement was timely submitted to the IRS and received a determination letter in early 2008 conditioned on the plan's timely adoption of some minor additional amendments within the period set forth under 401(b). The Plan has not yet adopted the amendments. Can such a failure be corrected under EPCRS's nonamender provisions or does the fact that the plan arguably does not have a valid determination letter impair its ability to rely on EPCRS? Is there some other procedure outside EPCRS for fixing what I would think could be a fairly common slip up but not one I have encountered before? Thanks.