update API Discovery's ongoing nature (#19476)

src/content/docs/api-shield/security/api-discovery.mdx

@@ -55,7 +55,7 @@ By adding endpoints to Endpoint Management, you will unlock further [security](/
 
 To restore any errantly ignored endpoints, you can filter by **Ignored** and select **Restore**.
 
-Check back regularly for new API Discovery results. A badge with the number of endpoints needing review will show in the API Shield dashboard.
+API Discovery is an ongoing process. Check back regularly for new API Discovery results. A badge with the number of endpoints needing review will show in the API Shield dashboard. You may see the quantities in the **Needs Review** and **Ignored** metrics change over time. As your actual API or traffic patterns to your APIs change, API Discovery results that are not saved can disappear.
 
 :::note