Benefit before and after merger

[Guest jhengle]

Under Code USC 1058 - The benefit a participant received after a pension plan is merged must be equal to or greater than benefit she was entitled to receive before the plan merger.

In Jan. 1996 a terminated participant requested his lump sum pension using PBGC rate and 1984 Mortality table, his amount to be distributed is $58,000, without his knowledge, in Feb of 1996 his plan is merged and the successor plan is using the code 417 accurrial assumption as amended by Gaat-RPA 1994 to determine lump sum values. In March he received his lump sum distribution of $48,000 from the successor plan sponsor.

Is 1058 violated? Does 411(d)(6) protect the lump sum amount due prior to the merger?