Can empty phplist_listattr_attrNN tables be safely deleted?

I have 6 empty “phplist_listattr_attrNN” tables in my database.

I am thinking they are leftovers from a much earlier version of phpList. But who knows. Something may have also been accidentaly dropped when I exported and reimported my data in the past.

What are they, and can these empty tables be safely deleted to clean up my database?

I do use a many user attributes, many which are active.

Thank you!