American Woodturner has an article on plagiarism i the latest edition.
There are obviously problems attached to this area of legal usage.

The example used in the article is a piece by Rude Osolnik as opposed to
a "knockoff" by someone else.

First: How on earth can Rude Osolnik prove to anybody that _his_
piece is the first?
Where did he get the idea?
Who else did almost the same at different points in time without
being registered by the author of the article?
As a point of interest, I would think that quite a few such objects
have been made since 1960, the form being a typical 60ies thingy.
Neither is it especially complicated, so, in my judgement a lot of people
could have made the thing independently without knowing about any
of the others.
Are we then speaking plagiarism?

In my opinion the fact that a piece has been sold by somebody does not
create copyright unless you can document being "the first".

In my opinion it is not enough to be the first in your neighborhood to
make a certain form, to establish copyright, or the right to deem others
"knockers off". The techniques and the materials are pretty universal,
and the one hollow form does not differ too much from the other,
unless, and here is one point that I feel is important:
Unless the technique is so complex and the choice of materials and
the finishing touches are so distinct and rare that little doubt can be
had as to the originality of the work.

Collectors value was mentioned, and the copies was said to diminsh
the value of the original.
This I can not understand:
Like the collectors of sculpture and painting, there are two significant
ways to establish the value and origin of a piece:

The signatu
If a piece is signed, and someone else copies the work _and_
the signature, then I imagine that existing laws in all countries
have been breeched, and a lawsuit is a near possibility.

The technique:
If the artists technique is sufficiently complex and special that
an expert or two can examine the work, and state that the probability
of the piece being an original from this or that artist, then the
probability may be worth the money.
Sometimes the copy brings as much money as the original,
even though "everybody" knows the piece to be a copy, it is
that interesting, or well made.

I think this "problem" of plagiarism is a bit out of proportion.
Expensive, well known pieces that are well documented by the
artist or the gallery is one thing: There the term plagiarism may
have some meaning.

Undocumented "firsts" or very local "firsts" of simple form
and common materials should be treated as "public domain"
because of the problem of establishing a real "first".
If the artist signs his pieces and documents his production in a
satisfactory way, he is, of course, in a better position to grumble
about "knockoffs", but it is my opinion that the form cited
in American Woodturner as being an "Osolnik" is far too simple
both in the form and in the choice of material to represent
a real "first".

Bjarte