the rule “Windows Services” is for your thresholds, that means for already existing Services.
It’s pretty easy to say if it’s a “threshold”-rule by looking at the bottom of the page while creating/editing a rule.
If there is a “Name Of The Service”-Section, it’s focused on already existing services.
So, with “Windows Service Discovery” you can let Check_MK create Services based on the information from the Check_mk Agent. If your “service” there is missing, it won’t find anything to create.
For this point, it’s important that your allowing the section “Installed, stopped and running services” for your agents:
“Windows Services” ← Threshold rule, based on existing services (like saying, it’s OK if it is stopped)
“Windows Service Discovery” ← Creating services based on a regex and the agent output