If they did not complain when they were sent the letter (of vesting) either they did not care about the stock or was under the same assumption they were that is over 4 years.

Of course, contracts are legally binding, but that's completely different from my perception / evaluation of someone - if the mutual understanding was over 4 years and then 30 years later you find the typo and come back to bite me then yes it is 100% an irreparable relationship.

Yes I would think better of them if they came back to bite if NVIDIA was a penny stock but probably nobody would bite them back if they found out it was worth $100 instead of $1B.

To be clear, the grant is the legally binding document regardless of intent (initial offer + vesting seems to imply 4 years), I would eat the typo if it was 30 years ago and chalk it off as a learned mistake (assuming it wasn't company altering), although I would still think less of them for fleecing.