Non-PRO FVA Not for points Japanese to English Tech/Engineering Business/Commerce (general) quantity

I've seen the term "1 pcs" frequently in documents translated from Japanese to English. The term refers to quantity, and "pcs" means "pieces" from the context apparently.
First I thought it is just a common mistake Japanese people often make...but I've seen this expression several times on English websites.
Why do they use a plural form? I'm wondering if it is a commonly used or accepted expression...I mean, it's not grammatically correct, is it?
Is this expression a kind of jargon? I'd like to know.

Thanks.