[QUESTION] Inconsistent cell labelling?

Hi, I have been playing around with `cellxgene_census 1.17.0` running on macOS. I am very interested in exploring the relationships between cells types but I have a few questions concerning the annotations. Specifically, I am running: ``` import cellxgene_census cell_meta_data = cellxgene_census.get_obs( census, "mus_musculus", column_names=["cell_type"] ) cell_meta_data = cell_meta_data['cell_type'].value_counts() ``` When I look at the cell list, I noticed that there are a few inconsistencies in the entries. Some have a double quotes while most don't which could become problematic for consistent string parsing. But my main question is related to 2 specific entries, namely the "unknown" and the "cell" one. What are these supposed to represent in the census? Is there a reason they were retained? Thank you for your help.