EPS - For how may years the NRS form is to be filled in order to avail the scheme certificate?

When we fill form 10 C for employee who has left after 30 years of service we also have to fill one statement of non reckonble service (NRS) . Kindly let us know as to up to what period this NRS form is to filled . As the EPFO authorities are asking to fill the form for all the thirty years of service and as of now we do not have such old records, as we are a very small unit. We have record for the last about 15 years .
My question is : For how may years the NRS form is to be filled in order to avail the scheme certificate. What is the mandatory requirement .

NRS form needs to be filled at least last 12 months from the date of exit. In case of death in service it is necessary either to fill for EDLI