Update manage-certificates.mdx

clarification around zone-level AOP cert management

Author: chris-martinelli

src/content/docs/ssl/origin-configuration/authenticated-origin-pull/set-up/manage-certificates.mdx

@@ -63,4 +63,11 @@ However, requests are dropped at your origin if your origin only accepts a valid
 
 2. [Check whether new certificate is Active](/api/resources/origin_tls_client_auth/methods/get/).
 
-3. Once certificate is active, [delete the previous certificate](/api/resources/origin_tls_client_auth/methods/delete/).
+3. Once certificate is active, [delete the previous certificate](/api/resources/origin_tls_client_auth/methods/delete/).
+
+:::note[Note]
+
+
+The API will say "active" for two certs if two are present, but the most recently uploaded certificate will be what's enabled and used.
+
+:::