Zigbee.db Table Structure

Out of curiosity, I opened up the zigbee.db database. I noticed a lot of duplicated tables with names like devices_v5, devices_v6 … up to devices_v11. The contents seemed almost the same, with just one field added on some of them.

Are these actively used, or are they left over from some database structure change? Can they be deleted? I guess it’s not hurting anything to leave them. It just seems untidy.