Retroactive plan amendments?

[John A]

Can either of the following situations be corrected by retroactive plan amendment:

1) In a 401(k) plan, deferrals were limited to 2% - 15% of compensation. Plan document did not specify the 2% minimum.

2) Plan was valued quarterly. Plan document specified annual valuation and did not give the option of other valuation dates.

In both cases, the plan has been operated consistently for ten years or so.

If retroactive plan amendments cannot be done, what would the corrections be?

What IRS program under Rev. Proc. 2001-17 would be used?