Why does the Docker image seem older than the latest npm release?

I'm running 9router in Docker and noticed that the version shown by the npm package appears much newer than the image I get with decolua/9router:latest. The dashboard also checks npm for updates, so it keeps showing an update notification, while the "Update now" action runs npm i -g 9router@latest, which doesn't actually update the server being run from the container. Is the Docker publishing process delayed, or does the latest tag simply not reliably point to the newest release? Should Docker users pull an explicit version tag, build their own image, or use a different update method?