Read the definition of early and normal retirement in the document it will answer this question.
If it is like most plans I see the definition will be ANY termination after being a given age and/or service.
Rarely does it define it any other way. So my guess (and it is a guess at this point) is you will find upon careful reading of the document that they did retire.
Have you considered negotiating a contract modification? The company I work for (also in the group annuity plan business) would rather change (older) contracts than lose a client.
Sometimes people get this confused with crediting prior service for VESTING purposes. Perfectly ok to exclude service prior to establishment of the plan for VESTING. Not for eligibility, as WCC mentions. You might want to check your document 'cause I suspect that the exclusion for prior service may be for vesting.
From the EOB: All service with the employer must be credited, even service before the plan is established, unless disregarded under the break in service rules
See IRC §410(a)(5)(A)
service for eligibility purposes cannot be excluded unless under the above referenced break in service rules