I found this "blog" where the point I refer to is fully explained. http://englishharmony.com/past-participle-as-adjective/
Since the moment I read it, I've been wondering if
It was already burned when I came here.
shares the same meaning as
When I came here, it had already been burned.
I don't know whether my examples are correct. If you have a look at the website above-mentioned, you will see the examples given, which are
'He is gone' . Vs.
"He has gone'.
If they mean the same, theoretically, in addition to the examples I gave you at the beginning of my question, I might say
" He was gone' / "he had gone"
couldn't I? The choice depends on the context, according to that blog.