MrMC

I am not sure I understand the question but I'll try to give some pointers on how DB works...

V16 database is copied and updated to v17 first time you run kodi v17 or MrMC 3.*.*

If you have MySQL setup, and you have tested any beta/rc kodi or TestFlight MrMC 3 your database has been updated at that time, unless you move all your clients to v17 db, you will be missing watched/unmatched status synchronization and library updates(assuming only one client is setup to do updates.

16 and 17 are not compatible and two don't see each other, database names are different.

Hope it helps...

V16 database will only be copied once, first time you run MrMC 3.0.0, and never again until you remove database from MySQL server.

MrMC appends database version number to the end of database name, so in 3.0.x if you name database "MyVideos" in settings actual name on MySQL server will be "MyVideos106"(I think) and MrMC 2.x.x database name will be "MyVideos99". That's the reason why you are not seeing newly added videos on version 3.0.x