Pension Payout Issue

[Guest MC2]

A participant of a multiemployer pension plan recently passed away. The participant's benefits were 100% vested. The participant, however, stopped working for a contributing contractor in 1979. Should the plan refer to the plan document that was in effect when the participant last worked (i.e., 1979) or the current document in determining whether the participant qualifies for a death benefit to be paid to his beneficiary?

Thanks!