diff --git a/api/TimeAddressableMediaStore.yaml b/api/TimeAddressableMediaStore.yaml
index c5284280..1d2601cc 100644
--- a/api/TimeAddressableMediaStore.yaml
+++ b/api/TimeAddressableMediaStore.yaml
@@ -2003,11 +2003,10 @@ paths:
         A service instance MAY support Media Objects that are held in external storage in another TAMS or other media storage system.
         The Flow Segment may in that case require the `get_urls` property to provide the information needed by clients to access the Media Object.
 
-        Clients MAY modify Flow Segments, but this should only be done in exceptional circumstances to correct metadata as such operations will likely break the idempotency of Segments.
-        Properties of Media Objects, such as `get_urls`, SHOULD be modified via the [`/objects`](#/operations/GET_objects) endpoints.
-        They SHOULD NOT be modified at this endpoint, and TAMS instences SHOULD reject such requests with a `400` error.
+        The list of instances of an object (and associated `get_urls` entries) can be modified via the [`/objects`](#/operations/GET_objects) endpoints, which provides a mechanism to register new instances of an object.
 
-        If a client needs to modify a Flow Segment, e.g. to correct metadata such as the `key_frame_count` or add additional URLs to `get_urls`, then the client SHOULD first delete the existing Segment and then write a new one.
+        Clients MAY modify Flow Segments, but this should only be done in exceptional circumstances to correct metadata such as `key_frame_count`, as such operations will likely break the idempotency of Segments.
+        If a client needs to modify a Flow Segment, then the client SHOULD first delete the existing Segment and then write a new one.
         The behaviour is undefined if the Segment exists and the service may return a 400 error response.
 
         For successful creation of all Segments in the request a 201 response should be provided.
@@ -2016,11 +2015,13 @@ paths:
 
         Clients are expected to decide how to break content into Media Objects, however those Objects SHOULD be large enough to avoid excessive round trip overheads in the underlying store (_e.g._ of the order of several megabytes) and where codecs with temporal re-ordering are used, Object SHOULD contain complete GOPs or decodable units.
 
-        For Media Objects that have been re-used from other Flows, the `sample_offset` and `sample_count` MAY be used to specify part of the Media Object to use:
+        For Media Objects that have been re-used from elsewhere, the `sample_offset` and `sample_count` MAY be used to specify part of the Media Object to use:
           - The `timerange` field indicates the new Segment's position in the Flow
           - The sample associated with the start of the `timerange` MUST be the one selected by `sample_offset`
           - Likewise, the sample associated with the end of the `timerange` MUST be the one selected by `sample_offset + sample_count - 1`, unless `timerange` has an exclusive end, in which case it will be  `sample_offset + sample_count`.
           - The timerange of the Segment MUST NOT overlap any other Segment in the same Flow.
+
+        When re-using Media Objects, requests which change object properties (e.g. `key_frame_count`) SHOULD be rejected.
       operationId: POST_flows-flowId-segments
       tags:
         - FlowSegments
diff --git a/docs/appnotes/0018-managing-multiple-object-instances.md b/docs/appnotes/0018-managing-multiple-object-instances.md
index b7a50850..e967ead5 100644
--- a/docs/appnotes/0018-managing-multiple-object-instances.md
+++ b/docs/appnotes/0018-managing-multiple-object-instances.md
@@ -108,12 +108,13 @@ Example POST body to `/objects/{objectId}/instances`:
 
 ### Deleting an Object Instance
 
-Specific instances of a Media Object can be deleted by a DELETE request to `/objects/{objectId}/get_urls` with the relevant `storage_id` in the query string.
+Specific instances of a Media Object can be deleted by a DELETE request to `/objects/{objectId}/instances` with the relevant `storage_id` in the query string.
+However attempting to delete the last instance of a media object should be rejected: this requires deleting the referencing Flow Segments instead.
 
 Example DELETE request:
 
 ```text
-http://tams.example.com/objects/846023d3-612d-5014-bc47-88f6eb2d04bb/get_urls?storage_id=323367fd-21bb-4f2e-ad38-faf048c4ccfc
+http://tams.example.com/objects/846023d3-612d-5014-bc47-88f6eb2d04bb/instances?storage_id=323367fd-21bb-4f2e-ad38-faf048c4ccfc
 ```
 
 Once deleted, this instance will no longer be advertised in `get_urls` on the `/objects/{objectId}` endpoint or on the `/flows/{flowId}/segments` for Flow Segments which use the Media Object.