[Milhouse]

However, lets say you have Kodi 18 on one box and Kodi 17.6 on another and you use the same advancedsettings.xml both versions will create their respective database on MySql when you add the sources from Kodi for each. So if you already had V18's database adding V17.6 should create new databases in MySql for Kodi 17.6. Is this correct?

Yes, but they'll be independent databases, so there'll be no syncing between clients on different versions, which is usually what most users want/expect when using multiple clients and a shared database (singular). You might as well use SQLite and forget about MySQL in the scenario you describe.