diff --git a/eos/file_reader.py b/eos/file_reader.py
index 28d6459..56d8f16 100644
--- a/eos/file_reader.py
+++ b/eos/file_reader.py
@@ -605,8 +605,9 @@ class AmorEventData(AmorHeader):
             output = np.recarray(a1.shape[0]+a2.shape[0], dtype=new_fields)
             for field in new_fields.fields.keys():
                 output[field] = np.concatenate([a1[field], a2[field]])
-            logging.warning("Missing data when combining datasets, "
-                            f"{tuple(a1.dtype.fields.keys())} != {tuple(a2.dtype.fields.keys())}")
+            logging.warning("      Missing data when combining datasets,\n"
+                            f"          {tuple(a1.dtype.fields.keys())} \n"
+                            f"        !={tuple(a2.dtype.fields.keys())}")
             return output
 
     def append(self, other):
@@ -626,7 +627,15 @@ class AmorEventData(AmorHeader):
         else:
             new_device_logs = {}
             for key, slog in self.data.device_logs.items():
-                olog = other.data.device_logs[key]
+                try:
+                    olog = other.data.device_logs[key]
+                except KeyError:
+                    if getattr(other.experiment, 'end_date', None) is None:
+                        logging.warning(f"      Device logs for '{key}' not found in dataset to be added, "
+                                        f"ignoring key as file is not finalized")
+                        continue
+                    else:
+                        raise KeyError(f"Device logs for '{key}' not found in dataset to be added")
                 new_device_logs[key] = np.recarray(slog.shape[0]+olog.shape[0],
                                                    dtype = slog.dtype)
                 new_device_logs[key].time = np.concatenate([slog.time, olog.time])