Amusingly, this identical vague mechanism was given 2 different names: "Management top slice" when talking to investors/managers, and "Engineering top slice" when talking to the engineering staff.
This ridiculous mechanism was never defined (and ultimately no acquisition occurred in that time-frame), arguments over it ultimately may have helped a few engineers get out so that was about all the impact it had.
The lesson is not to count on verbal agreements. If they don't put anything on paper it's because they don't want to and don't value you enough to care, not because "the time isn't right" or similar nonsense.
