As per tradition, one has to perform Pitru tarpaNam for 96 days in a year. This is known as shaNNavati tarpaNam which includes 16 days of mahAlaya tarpaNam.
The annual pratyAbdika SrAddha is different from the one performed at GayA. There is no pramANam for abandoning the annual SrAddha or MahAlaya Tarpanam once GayA SrAddham is done. According to the Scriptures, these have to be performed till one is alive.