The unofficial "pattern" tends to be:
- X.0 normal support term
- X.1 extended support term
- X.2 normal support term
- X.3 extended support term
- X.last-release extended support term
Thus, if X.3 is the last release, it's an extended support release.
If there's an X.4, that is usually the final release, so it's an extended release.
These days (since 5.0) it's rare to get more than 4 minor releases.