The well-written ones, anyway. What is the answer if the amendment just changes the schedule as of the amendment's effective date and says nothing about former employees or hours on or after or anything?
I for one think they are stuck and have to give the wind fall to the terminated person if they just talk about the effective date. If someone is mad look to the person who drafted the amendment. Being careful and drafting it to only include people who worked 1 hour after a given date is vesting amendment writing 101 and I find the sloppy writers learns the hard way only after making the sloppy mistake once.