Problem/Motivation
I just ran into a confusing situation which I only understood after looking into the code.
The goal is to migrate a Drupal 7 website to Drupal 10.
I started with the core migrate UI.
This creates migrations named like `d7_node_complete__blog`.
It also created some migrate map tables like `migrate_map_d7_node_complete__blog`.
These tables were filled with records, and the entities were created in the D10 database.
I noticed that I need a few additional modules to get a more complete migration, e.g. for views.
Then I started over, this time using the command from migrate_upgrade.
The hope was to simply add anything that was missing from the previous attempt.
However, thanks to the automatic prefix, new migrations were created, instead of reusing the existing ones.
The new migrations are named like `upgrade_d7_node_complete_blog`.
So I kept wondering why migrate:status reports everything as "not imported", when the migrate map tables were already filled.
Steps to reproduce
Start with a core migration from D7.
Then install this module and run `migrate:upgrade`.
Proposed resolution
I think all we need is some documentation.
Maybe this issue can already be enough :)
I think I am still scratching the surface here, so I cannot give a complete explanation at this moment.
But if I understand better what is going on, I might post a reply here with more info.
Remaining tasks
User interface changes
API changes
Data model changes