Defect-based testing is a powerful tool for finding errors in software, including medical device software. Many software manufacturers avoid this method because it requires a detailed defect taxonomy that is expensive to construct and difficult to validate. SW911 is new defect taxonomy for health software being developed by the Association for the Advancement of Medical Instrumentation. This paper explains how defect taxonomies have been used and the benefits to industry. The initial steps of the validation of SW91 include mapping vulnerabilities from the Common Weakness Enumeration and a dataset from a medical device software development company in Ireland. Finally, the paper details future plans for validation, including taxonomy based testing which will be used to validate the efficiency, reliability, ability to perform useful analyses and defect coverage of SW91.