When choosing any Period for a maintenance or audit, a start date which only allows a single instance to be scheduled in the same calendar will cause any subsequent maintenance to be created for the same month and day of the next year.
Start Date: 10-01
Choosing this start date only leaves three months left in 2020 instead of the four that are needed. The function will create a maintenance/audit on 2020-10-01 and 2021-10-01.
A minor suggestion on the Periods: You may want to rename “Semester” to “Semiannual”.