As none of us users here is an engineer off the team, neither I nor most of the folks here can answer that in perfect technical detail. Trust me, it's been asked ... by a lot of us. I've never heard a definitive answer even from the engineers attending NAB.
For practical terms, the Media Browser is clearly the most stable method of getting the media and all metadata from and about that media into the project file. Importing by right-clicking blank space in the Project panel and selecting import is about as good, but maybe not always. Still, that method has the joy of importing the folder structure of the media on disc as bins, which ... is meta in its own way, right? And seems to nearly always work perfectly.
Those are the only way I'll import anything, as well ... the burned hand teaches best, right?
And I never ever EVER drag/drop a clip into PrPro from "explorer", the Windows file manager. Ahem ... talk about a badly burned hand ...
Agreed. Like I said, I just learned that importing via the MB is the ONLY way to setup the files so that Premiere "knows" that a file in an imported sequence already exists in a project. But I haven't been able to find anything that indicates why the browser method is any different than the right click. Except that it is.
In most of the documentation and tutorials, all the import methods are treated as equal. But they obviously are not.
You're right, they're not treated the same internally. No clue, but ... one learns to do what works in practice and ignore what should work in theory ... sigh.