Are vulnerabilities ever deleted from NVD?
No. Vulnerabilities that are rejected by the Common Vulnerabilities and Exposures (CVE) standard vulnerability dictionary (e.g. because they are duplicates) are labeled as such in the description with an explanation of the problem. The vulnerability attribute fields are then cleared. The NVD web site will always show a web page for rejected vulnerabilities if you send that CVE name in the URL but will never include them in a search result. In the NVD XML feed, rejected vulnerabilities have the “reject” attribute within the entry field equal to “0”.