Hi,
Accidently put my reply in quote, I worry SF Team missed out so that I reply again.
For 1 and 2, it sounds like you deleted a database in between the first and second deployment without clearing the object name history. That's the most common reason for the type of error you are seeing in your log file.
For 1, we create a NEW package as a replacement of the OLD one. For example, we create package A, import database A, deploy to customer. After few months later, we lost the package (for example), and at that time, no database structure changes made. Then, we recreate the whole new package, import database and deploy. We expected would able to upgrade the existing database which created using OLD package. However, we hit the error as attached in previous post.
Beside, if I have existing database that already deployed to customer, can I use DDT to upgrade them in the future since it is not created by DDT?
For 2, yes, we did remove the object history. However, the error is still happening.
For 3,the security import is only designed to be done once for a databse. You do not need to re-import the tables every time your data changes, the data packages will be refreshed whenever you recreate a deployment package (assuming you don't select "No" when it prompts you to package deployment data).