If for any reason it is determined that any eligible retirement system employee was not given an opportunity to vote in the referendum conducted with respect to the retirement system of which he was a member at the time of the referendum, or that an employee who was permitted to vote in such referendum was not an eligible retirement system employee at that time, such determination shall not invalidate the results of such referendum if a majority of the eligible retirement system employees under such retirement system voted in such referendum in favor of inclusion under the federal system.