Even then, pension fund payouts are still based on a projection of future returns, and also the future number of participants. Back during the subprime fiasco and the resultant market meltdown, there was a lot of media coverage of pension shortfalls, and also many threads here in this forum about the subject.
Technically, future payouts are determined by the pension calculation formulas. The fund solvency and ability to meet the commitments are determined by contributions, participants and future returns.