Is the calibration certificate number sufficient to control the calibration certificate issued to customers?  

The number helps you identify and trace the document, but is not the only control required. Each laboratory must determine the necessary controls for all documents and records to meet ISO 17025, customer and regulatory requirements. Calibration certificates require controls to ensure unique identification, indication of amendments, protection, back-up, archive, storage, retrieval, retention time, and disposal. An example of a control measure is protection against editing. Another example is to ensure the correct information is included to minimize any misuse or misunderstanding (see clause 7.8.2).

The Advisera ISO 17025 document template: Calibration Report and Certificate Requirements Procedure at https://advisera.com/17025academy/documentation/calibration-report-and-certificate-requirements-procedure/may be of interest.