410b coverage testing when plan is amended

[AKconsult]

Rev Proc 93-42 requires annual testing for 410(b) with the caveat that the snapshot day must be reasonably representative of the coverage throughout the year. What if the last day snapshot is not a reasonable representation? For example, I have a plan that was amended 11/1 to let in additional employees who were previously excluded. As of 12/31, the plan will pass the ratio percentage test.

However, had I performed the test on 10/31, they won't pass. It doesn't seem right that I can just test on 12/31 and say everything is fine when in truth there were 10 months during which some employees were excluded.

I can't find any guidance to explain how to do the testing in the year of a plan amendment that affects coverage.