retroactive plan amendment

[Gary]

a plan converted a db plan to a cash bal plan eff 1/1/2001.

the executed plan doc is 12/27/2001.

apparently there was a prior version of such cash bal plan (also w/ eff date of 1/1/2001) that may have been in effect from 1/1/2001 until 12/27/2001 when current version was executed.

the issue is that under first cash bal plan, the act equiv converted cash bal to annuity in such a way that pvab was greater than cash bal. and in subsequent plan the act equiv converted cash bal to an annuity such that pvab was less than cash bal account.

plan paid cash bal account in all situations.

question is: should the accd ben under prior act equiv be preserved through 12/27/01 and thus if pvab greater (using old act equiv) than cash bal, then pvab s/b paid?

or can plan retroactively apply the 12/27/01 amendment eff as of 1/1/01 and not be required to pay pvab under old and greater basis?

look forward to other interpretations.