The Sequence Number plugin has undergone a change some time ago, with regards to its default name in the database (which can be overridden using the key property).
Before the change, it used to create an entry in the database matching the full path (id property) of the Sequence Number model (this is what we see in the first 2 bullets).
Following the change, it creates an entry matching the model name (name property) - this is probably what we see in bullet 3 (unless that one uses the key property).
The different behavior is actually controlled by the pluginVersion property, which if set to 1 employs the new behavior, were as if absent displays the old behavior.
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