How does the compliance calendar know what each company owes Companies House?

Company Secretarial → Compliance calendar lists, in date order — overdue, due soon, upcoming — three sources: Companies House's own next accounts and confirmation-statement dates (read in the register sync), the statutory clocks a resolution starts (e.g. a form within fourteen days of an appointment — only clocks computable from the resolution date are scheduled), and deadlines a person added with Add a deadline. Refresh from Companies House re-reads the published dates. A moved deadline marks last year's row not required rather than deleting it.