Magical Pokemon Journey - English version of manga lost

I feel like that isn't a very good definition of lost media. Firstly, "inaccessible to the general public" is too vague to serve as a definition. It could include media that was never released to the public, as well as media that was released physically, but now is out-of-print, exists in limited numbers, and never uploaded to the surface Internet.

Secondly the quote you provided itself makes a distinction between media that's lost and media that's hard to find or inaccessible. It thus fails to establish that something falls under the category of lost media just because you can't immediately find it. It's also intuitive that just because something is "hard to find," it's not necessarily lost. Plus, if you conflate all these categories mentioned in the quote, it becomes immediately clear that this isn't what people mean when they say "lost media."

The series in question can easily be classified as "out-of-print," and I don't think it's reasonable to suspect that the last two missing volumes were were all destroyed, so in my view, calling it "lost media" is misleading.