MCLC: dissent speaks code (10)

[Denton, Kirk]

MCLC LIST
From: Costas Kouremenos <enaskitis at gmail.com>
Subject: dissent speaks code (10)
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Dear Wolfgang,

thank you for the explanation. Similar sentences in my book (by XU Dan)
are these:

他被压了一条腿
One of his thighs was crushed

她被人抓住头发不放
A man grabbed her by the hair and wouldn't let it(her) go.

Xu Dan describes it in different terms, but it's the same thing. He says:

"In a bei construction, the noun group that follows the verb is often
semantically a inherent part of the patient (=subject)."

I have a question concerning your example. Instead of your interpretation:

郭威被刺污了臉儿
(lit.: "Guo Wei was stabbed-from-dirt the face")
"Guo Wei had the dirt scraped off from his face"

isn't the following also possible:

"Guo Wei's face was smeared by thorns"

where the sentence has an agent, too? Is this outright wrong, or just to
be rejected because of the context?

Lastly, something someone already asked days ago: When did "bei" start
having a usually negative, 'inflictive' connotation? Or was it right from
the beginning?

Best, Costas