`vat_registration_start` and `vat_registration_end` (partial VAT periods)
vat_registration_start and vat_registration_end (partial VAT periods)
vat_registration_start and vat_registration_end are optional dates in YYYY-MM-DD form, stored in datapackage.json under busdk.accounting_entity and set via bus config. They record when the entity became VAT registered or ceased to be registered. The bus vat module uses these as inputs when it builds the sequence of VAT periods; that sequence can include partial first or last periods, transition periods (e.g. 4 months), and non-standard lengths (e.g. 18-month first period). Bus-config only stores the dates; period boundaries are defined by bus-vat. See Vero: Arvonlisäveron verokausi ja sen muutokset. Omit both keys or set them to null when not applicable.