Older versions of Grafana were not previously discovered, because an update somewhere between 6.4.3 and 6.7.2 changed the frontend code for revealing the version of Grafana being used:
<a href="https://grafana.com" target="_blank">Grafana</a><span>v6.4.3 (commit: 3a2bfb7)</span> for example.
Even older code did not use any explicit HTML.
This new regex correctly detects all versions of Grafana, from 1.0.0 to the current version.