code: func (ps *prometheusState) isOutdated(collector *collector) bool {
  	labels := collector.labels
  
  	if entrypointName, ok := labels["entrypoint"]; ok && !ps.dynamicConfig.hasEntrypoint(entrypointName) {
  		return true
  	}
  
  	if backendName, ok := labels["backend"]; ok {
  		if !ps.dynamicConfig.hasBackend(backendName) {
  			return true
  		}
  		if url, ok := labels["url"]; ok && !ps.dynamicConfig.hasServerURL(backendName, url) {
  			return true
  		}
  	}
  
  	return false
  }
docs: // isOutdated checks whether the passed collector has labels that mark
  // it as belonging to an outdated configuration of Traefik.