PBGC Covered?

[stbennet]

First year of a cash balance plan with 26 active participants using the plan's definition. However, only 23 participants actually received a hypothetical account allocation. Using the "benefit liabilities" definition of participant ala the PBGC premium filing the plan would qualify for the professional service organization exemption.

I know they wouldn't have a premium due in the first year regardless, but does anyone have experience with this type of situation? Would they be required to file?