diff --git a/src/spyglass/spikesorting/analysis/v1/group.py b/src/spyglass/spikesorting/analysis/v1/group.py
index 477f32c75..b46ee1b0b 100644
--- a/src/spyglass/spikesorting/analysis/v1/group.py
+++ b/src/spyglass/spikesorting/analysis/v1/group.py
@@ -133,11 +133,8 @@ def fetch_spike_data(key, time_slice=None):
                 include_unit = SortedSpikesGroup.filter_units(
                     group_label_list, include_labels, exclude_labels
                 )
-                sorting_spike_times = [
-                    times
-                    for times, include in zip(sorting_spike_times, include_unit)
-                    if include
-                ]
+                from itertools import compress  # worth bumping to top of script
+                sorting_spike_times = list(compress(sorting_spike_times, include_unit))
 
             # filter the spike times based on the time slice if provided
             if time_slice is not None:
diff --git a/src/spyglass/spikesorting/imported.py b/src/spyglass/spikesorting/imported.py
index ef6d60900..e397ee95e 100644
--- a/src/spyglass/spikesorting/imported.py
+++ b/src/spyglass/spikesorting/imported.py
@@ -86,18 +86,18 @@ def add_annotation(
         merge_annotations : bool, optional
             whether to merge with existing annotations, by default False
         """
-        if not len(self & key) == 1:
-            raise ValueError("ImportedSpikeSorting key must be unique")
+        if isinstance(label, str):
+            label = [label]
+        query = self & key
+        if not len(query) == 1:
+            raise ValueError(f"ImportedSpikeSorting key must be unique. Found: {query}")
         unit_key = {**key, "id": id}
-        if ImportedSpikeSorting.Annotations & unit_key:
-            if not merge_annotations:
-                raise ValueError("Unit already has annotations")
-            existing_annotations = (
-                ImportedSpikeSorting.Annotations & unit_key
-            ).fetch(as_dict=True)[0]
-            existing_annotations["label"] = (
-                existing_annotations["label"] + label
-            )
+        annotation_query = ImportedSpikeSorting.Annotations & unit_key
+        if annotation_query and not merge_annotations:
+            raise ValueError(f"Unit already has annotations: {annotation_query}")
+        elif annotation_query:
+            existing_annotations = annotation_query.fetch1()
+            existing_annotations["label"] += label
             existing_annotations["annotations"].update(annotations)
             self.Annotations.update1(existing_annotations)
         else:
@@ -130,11 +130,12 @@ def fetch_nwb(self, *attrs, **kwargs):
         nwbs = super().fetch_nwb(*attrs, **kwargs)
         # for each nwb, get the annotations and add them to the spikes dataframe
         for i, key in enumerate(self.fetch("KEY")):
-            if ImportedSpikeSorting.Annotations & key:
-                # make the annotation_df
-                annotation_df = (self & key).make_df_from_annotations()
-                # concatenate the annotations to the spikes dataframe in the returned nwb
-                nwbs[i]["object_id"] = pd.concat(
-                    [nwbs[i]["object_id"], annotation_df], axis="columns"
-                )
+            if not ImportedSpikeSorting.Annotations & key:
+                continue
+            # make the annotation_df
+            annotation_df = (self & key).make_df_from_annotations()
+            # concatenate the annotations to the spikes dataframe in the returned nwb
+            nwbs[i]["object_id"] = pd.concat(
+                [nwbs[i]["object_id"], annotation_df], axis="columns"
+            )
         return nwbs