Eric didn’t post the full stock option agreement, only its cover sheet. Given the language of the 1996 termination letter, it’s a good guess that the full agreement specified expiration 90 days after termination.
In another case I was paid out and my options supposedly terminated when a company I worked for was acquired by Splunk. The startup had used Carta to manage the options and nobody terminated the agreements in Carta and I kept vesting. The joke was I was going to wait to fully vest and then ask them to convert to Splunk stock. Someone eventually noticed and they revoked all agreements in the system. I still wonder how that would have played out legally, but I also wasn't interested in double dipping.