diff --git a/stix2/datastore/filesystem.py b/stix2/datastore/filesystem.py
index 95c9050..3b518b7 100644
--- a/stix2/datastore/filesystem.py
+++ b/stix2/datastore/filesystem.py
@@ -223,14 +223,19 @@ def _get_matching_dir_entries(parent_dir, auth_set, st_mode_test=None, ext=""):
     results = []
     if auth_set.auth_type == AuthSet.WHITE:
         for value in auth_set.values:
+            filename = value + ext
             try:
-                filename = value + ext
-                s = os.stat(os.path.join(parent_dir, filename))
-                if not st_mode_test or st_mode_test(s.st_mode):
+                if st_mode_test:
+                    s = os.stat(os.path.join(parent_dir, filename))
+                    type_pass = st_mode_test(s.st_mode)
+                else:
+                    type_pass = True
+
+                if type_pass:
                     results.append(filename)
             except OSError as e:
                 if e.errno != errno.ENOENT:
-                    raise e
+                    raise
                 # else, file-not-found is ok, just skip
 
     else:  # auth_set is a blacklist
@@ -246,12 +251,17 @@ def _get_matching_dir_entries(parent_dir, auth_set, st_mode_test=None, ext=""):
                 continue
 
             try:
-                s = os.stat(os.path.join(parent_dir, entry))
-                if not st_mode_test or st_mode_test(s.st_mode):
+                if st_mode_test:
+                    s = os.stat(os.path.join(parent_dir, entry))
+                    type_pass = st_mode_test(s.st_mode)
+                else:
+                    type_pass = True
+
+                if type_pass:
                     results.append(entry)
             except OSError as e:
                 if e.errno != errno.ENOENT:
-                    raise e
+                    raise
                 # else, file-not-found is ok, just skip
 
     return results
@@ -325,9 +335,25 @@ def _search_versioned(query, type_path, auth_ids):
                     results.append(stix_obj)
             except IOError as e:
                 if e.errno != errno.ENOENT:
-                    raise e
+                    raise
                 # else, file-not-found is ok, just skip
 
+    # For backward-compatibility, also search for plain files named after
+    # object IDs, in the type directory.
+    id_files = _get_matching_dir_entries(type_path, auth_ids, stat.S_ISREG,
+                                         ".json")
+    for id_file in id_files:
+        id_path = os.path.join(type_path, id_file)
+
+        try:
+            stix_obj = _check_object_from_file(query, id_path)
+            if stix_obj:
+                results.append(stix_obj)
+        except IOError as e:
+            if e.errno != errno.ENOENT:
+                raise
+            # else, file-not-found is ok, just skip
+
     return results
 
 
@@ -341,7 +367,7 @@ def _search_markings(query, markings_path, auth_ids):
     :param auth_ids: Search optimization based on object ID
     :return: A list of all matching objects
     :raises TypeError: If any objects had invalid content
-    :raises IOError: If there were any problems opening/reading files
+    :raises IOError, OSError: If there were any problems opening/reading files
     """
     results = []
     id_files = _get_matching_dir_entries(markings_path, auth_ids, stat.S_ISREG,
@@ -355,7 +381,7 @@ def _search_markings(query, markings_path, auth_ids):
                 results.append(stix_obj)
         except IOError as e:
             if e.errno != errno.ENOENT:
-                raise e
+                raise
             # else, file-not-found is ok, just skip
 
     return results