Ongoing Vesting in Stock Sale

Company A buys Company B in a stock sale.  Company A's plan has no provisions for employer contributions.  Company B's plan has a discretionary match subject to a vesting schedule.  Company B's plan is to be merged into Company A's plan.  Under Company B, a participant is 60% vested under a 6-year graded schedule.  When the plan's are merged Company A's recordkeeper will need to set up a source for Company B's match, and the participant's match will need to be set up at 60%.  

Question.  Would I be correct that as the participant continues to earn vesting service the vesting for the account must increase accordingly.  Further, would Company A's plan need to be amended to accommodate the protected vesting for the merged Company B accounts?  

Thank you.

Yes vesting service continues and vested percentage will increase and by virtue of the plans merging there should be amendment to A for needed B provisions unless there is generic language in A that accommodates.

Thank you very much.