Can I perform Sarva Pitru Amavasya if I missed all the other Pitrupaksha days?

Yes. The scriptures specifically designate Sarva Pitru Amavasya as the remedy for missed rituals. If you were unable to observe any of the preceding Pitrupaksha days — due to illness, travel, work, or any other reason — performing the complete ceremony on Sarva Pitru Amavasya is considered a valid and complete fulfilment of your ancestral duty for the year.