The 'once only' principle 'means that citizens and businesses provide diverse data only once in contact with public administrations, while public administration bodies take actions to internally share and reuse these data' (source: http://toop.eu/once-only).
Govtracker has no evidence of progress on engineering systems to automatically comply with the 'Once-only' rule. However, this policy is included in the GDS plan for making better use of data. Moreover, the use of Verify will reduce need for duplicity in central government services.
Category: Public Services
Source: Manifesto - Page 81
Reference 1: Government Digital Service plan