The number scheme changed around 2014 when the numbers started getting close to -9999

https://cve.mitre.org/cve/identifiers/syntaxchange.html

Might as well add a massive 1000 prefix when upping the number of digits to catch truncating bugs early (seeing a bunch of 1000 is more obvious than if just the last of 5 digits is dropped)

Thousands of security issues don't even get CVE in a timely manner or lack details, or are not reported/included in the catalog at all. MITRE and NVD are overloaded and underfunded.

http://hackwolrdwide.com/7900-vulnerabilities-didnt-make-it-...