The rules under 1.410(a)-7(a) require that the employee's hire date be used to calculate periods of service for vesting purposes when the plan uses elapsed time for vesting.
For a new plan (not a successor plan) the law permits the plan to exclude for vesting purposes all service prior to the effective date of the plan.
Therefore there is a conflict between these rules which seems to be resolved by 1.410(a)-7(a)(3)(ii)(B) which states the true hire date may be 'adjusted' for periods of service not required to be counted. Although this may create multiple 'hire' dates, that is just the way it is.
Therefore, I conclude that if a plan uses BOTH elapsed time for vesting, AND excudes years prior to the effective date of the plan for vesting, then those hired before the effective date have an 'adjusted' hire date for vesting equal to the effective date of the plan.
Any disagreement on this?
Now to figure out how to make the software work!