newly covered employees and prior benefit stucture

[Draper55]

I have an expansion of the work force as of January 1.  These newly covered employees were previously excludables. Is it reasonable to disregard them with regard to the prior benefit structure under 401(a)(26) since they were not eligible to have accrued anything prior to 1/1. The cash balance book I have discusses this issue with regard to new plans; the same issue is involved here. Hard to imagine the force of 401(a)(26) is somehow to require the granting of past service credits upon entry to satisfy the prior benefit structure test. Short on time to research this in depth so any existing knowledge or thoughts would be appreciated.