We want to keep yearly tape backups for an infinite amount of time, but the year should not start at 1st january, but 1st march. For daily, weekly and monthly I can choose, when the day, week or month is starting. But I cannot choose when the year should start.

Is this not possible? I do not want a yearly backup at the time of 1st january, but 1-2 months later. 

We also have monthly full backups, which we keep for half a year. Should I just retain one from them as infinite manually?

Thanks!