Elective service crediting

[Scuba 401]

company A and B were part of the same controlled group and had one plan which has last day requirement.  company B splits off from A and establishes its own plan effective april 1 and mirrors all provisions.  company A does not want to fund matching contribution to those employees that went over to the Plan B because of the last day rule.  company B plan document credits prior service for vesting eligiblity and contribution allocation.  company B wants to fund the matching contribution to those employees that deferred in the controlled group plan prior the spinoff and they want to give the match for the entire year.  can they do this?   document credits service with company A for contribution allocation eligibility and vesting.

my feeling is the plan has a discretionary match so they can just say we are matching compensation deferred to all employees during the plan year or they can add specific language to that effect.