diff --git a/stix2/datastore/__init__.py b/stix2/datastore/__init__.py
index 57cb513..1ff0769 100644
--- a/stix2/datastore/__init__.py
+++ b/stix2/datastore/__init__.py
@@ -481,14 +481,14 @@ class CompositeDataSource(DataSource):
             if data:
                 all_data.append(data)
 
-        # remove duplicate versions
-        if len(all_data) > 0:
-            all_data = deduplicate(all_data)
-        else:
-            return None
+        # Search for latest version
+        stix_obj = latest_ver = None
+        for obj in all_data:
+            ver = obj.get("modified") or obj.get("created")
 
-        # reduce to most recent version
-        stix_obj = sorted(all_data, key=lambda k: k['modified'], reverse=True)[0]
+            if stix_obj is None or ver is None or ver > latest_ver:
+                stix_obj = obj
+                latest_ver = ver
 
         return stix_obj
 
diff --git a/stix2/test/v20/test_utils.py b/stix2/test/v20/test_utils.py
index 9372bbb..a66f3e8 100644
--- a/stix2/test/v20/test_utils.py
+++ b/stix2/test/v20/test_utils.py
@@ -114,7 +114,7 @@ def test_deduplicate(stix_objs1):
     mods = [obj['modified'] for obj in unique]
 
     assert "indicator--00000000-0000-4000-8000-000000000001" in ids
-    assert "indicator--00000000-0000-4000-8000-000000000001" in ids
+    assert "indicator--00000000-0000-4000-8000-000000000002" in ids
     assert "2017-01-27T13:49:53.935Z" in mods
     assert "2017-01-27T13:49:53.936Z" in mods
 
diff --git a/stix2/test/v21/conftest.py b/stix2/test/v21/conftest.py
index d602f42..a7a97a9 100644
--- a/stix2/test/v21/conftest.py
+++ b/stix2/test/v21/conftest.py
@@ -132,7 +132,13 @@ def stix_objs1():
         "type": "indicator",
         "valid_from": "2017-01-27T13:49:53.935382Z",
     }
-    return [ind1, ind2, ind3, ind4, ind5]
+    sco = {
+        "type": "url",
+        "spec_version": "2.1",
+        "id": "url--cc1deced-d99b-4d72-9268-8182420cb2fd",
+        "value": "http://example.com/"
+    }
+    return [ind1, ind2, ind3, ind4, ind5, sco]
 
 
 @pytest.fixture
diff --git a/stix2/test/v21/test_datastore_composite.py b/stix2/test/v21/test_datastore_composite.py
index 76119c3..c6128e5 100644
--- a/stix2/test/v21/test_datastore_composite.py
+++ b/stix2/test/v21/test_datastore_composite.py
@@ -59,6 +59,17 @@ def test_composite_datasource_operations(stix_objs1, stix_objs2):
     assert indicator["modified"] == parse_into_datetime("2017-01-31T13:49:53.935Z")
     assert indicator["type"] == "indicator"
 
+    sco = cds1.get("url--cc1deced-d99b-4d72-9268-8182420cb2fd")
+    assert sco["id"] == "url--cc1deced-d99b-4d72-9268-8182420cb2fd"
+
+    scos = cds1.all_versions("url--cc1deced-d99b-4d72-9268-8182420cb2fd")
+    assert len(scos) == 1
+    assert scos[0]["id"] == "url--cc1deced-d99b-4d72-9268-8182420cb2fd"
+
+    scos = cds1.query([Filter("value", "=", "http://example.com/")])
+    assert len(scos) == 1
+    assert scos[0]["id"] == "url--cc1deced-d99b-4d72-9268-8182420cb2fd"
+
     query1 = [
         Filter("type", "=", "indicator"),
     ]
diff --git a/stix2/test/v21/test_utils.py b/stix2/test/v21/test_utils.py
index 03477aa..f64cec2 100644
--- a/stix2/test/v21/test_utils.py
+++ b/stix2/test/v21/test_utils.py
@@ -104,17 +104,18 @@ def test_get_type_from_id(stix_id, type):
 def test_deduplicate(stix_objs1):
     unique = stix2.utils.deduplicate(stix_objs1)
 
-    # Only 3 objects are unique
-    # 2 id's vary
+    # Only 4 objects are unique
+    # 3 id's vary
     # 2 modified times vary for a particular id
 
-    assert len(unique) == 3
+    assert len(unique) == 4
 
     ids = [obj['id'] for obj in unique]
-    mods = [obj['modified'] for obj in unique]
+    mods = [obj.get('modified') for obj in unique]
 
     assert "indicator--00000000-0000-4000-8000-000000000001" in ids
-    assert "indicator--00000000-0000-4000-8000-000000000001" in ids
+    assert "indicator--00000000-0000-4000-8000-000000000002" in ids
+    assert "url--cc1deced-d99b-4d72-9268-8182420cb2fd" in ids
     assert "2017-01-27T13:49:53.935Z" in mods
     assert "2017-01-27T13:49:53.936Z" in mods
 
diff --git a/stix2/utils.py b/stix2/utils.py
index f741581..1b88f72 100644
--- a/stix2/utils.py
+++ b/stix2/utils.py
@@ -132,11 +132,12 @@ def deduplicate(stix_obj_list):
     unique_objs = {}
 
     for obj in stix_obj_list:
-        try:
-            unique_objs[(obj['id'], obj['modified'])] = obj
-        except KeyError:
-            # Handle objects with no `modified` property, e.g. marking-definition
-            unique_objs[(obj['id'], obj['created'])] = obj
+        ver = obj.get("modified") or obj.get("created")
+
+        if ver is None:
+            unique_objs[obj["id"]] = obj
+        else:
+            unique_objs[(obj['id'], ver)] = obj
 
     return list(unique_objs.values())