annotations: add sentence clarifying getMessage/history includes latest summary

Author: SimonWoolf

src/pages/docs/messages/annotations.mdx

@@ -505,9 +505,11 @@ await channel.annotations.delete(message.serial, annotation)
 
 ## Subscribe to annotation summaries <a id="subscribe" />
 
-The simplest way to receive annotation updates is via annotation summaries. A message that has annotations also includes a summary which is a synopsis of certain details of all annotations for that message. Summaries are updated in response to further annotation events for that message, and summary changes are delivered by default to subscribing clients.
+The simplest way to receive annotation updates is via annotation summaries. A message that has annotations also includes a summary, which is a synopsis of certain details of all annotations for that message. Summaries are updated in response to further annotation events for that message, and summary changes are delivered by default to subscribing clients.
 
-Annotation summaries are delivered to subscribers as messages with an `action` of `message.summary`, and a `serial` matching the `serial` of the message that they are updating. They have an `annotations` field which contains a `summary` of all the annotations for the message.
+When an already-existing message has an updated summary, the new version of that message will be delivered to subscribers with an [`action`](/docs/api/realtime-sdk/types#action) of `message.summary` (as opposed to `message.create` for the originally-published one), and a `serial` matching the `serial` of the original message. It will have an `annotations` field which contains a `summary` of all the annotations for the message.
+
+If you're not subscribing, you also retrieve the current version of a message, including the latest version of its summary, using [`channel.getMessage()`](/docs/api/rest-sdk/channels#get-message). Messages returned from [history](/docs/storage-history/history) also include the latest summary at the time the history request is made.
 
 The value of that `summary` field is an object where the keys are the [annotation types](#annotation-types). The structure of the value of each key depends on the summarization method used, for example `total.v1` will have a `total` field, while `flag.v1` will have `total` and `clientIds` fields.