Benefits would flux from year to year. Good years, benefits flex up for everyone drawing a pension. Bad years, benefits flex down for everyone drawing a pension.
How much flux depends upon the gates.
The nice thing about FedEx's management of our pension fund has been the realistic rate of returns and the continued contributions even when our plan met ERISA required levels. Way back in the dot.com days some of our pax brethren had companies predicting 10% or higher returns so no contributions needed and just got slammed in the financial tsunami.
Don't remember the timing, but FedEx recently reduced the expected rate of return. (think it's at 6% now)
It's something investors kinda pay attention to because excess profits on Pension funds can be used to artificially inflate company profitability and prop up stock prices