My elder sister Smt Saroja’s first annual ceremony will be this coming Karthikai month, sukla paksha trayodasi day. So far, all monthly and periodical ceremonies such as maasiyam and unam have been taking place properly. But, Karthika month sukla paksha trayodasi is not in the panchangam. Given this, how to conduct varushapthikam, unaaptikam, etc.? On which days must these be performed? We are clueless. Kindly clarify

As per the general scriptural approach, if a shraddha tithi is not available in the month of Karthikai, the annual ceremony must be performed during the preceding month. Because both Karthikai and Marghai have 29 days, it is common for a tithi to be missing during these months. If a shraddha tithi is not available during the months of Karthikai, Margazhi or Thai, the shraddham is performed during the month preceding these months, as per the rules of scriptures.
It is better to have these ascertained in advance.