It's fun for me to disscuss about this kind of topics.
Thank you for giving me the chance.

I think you are wrong in following piont.
"to the state of preservation of individual beads."

The defference of those type are not comming from the defference of preservation of individual beads.
It's clear and I'm sure.

I post same pictures again.
The beads in first picture and the beads in second picture are same kind of beads and both belong to type 1).
The defference of these beads are comming from the defference of the state of preservation of individual beads.
In this case you are right.

But type 1) and type 3) are different quality always.
Type 1) is roughlly designed in any case.
Type 3) is well designed in any case.
And you can find type 1) much more than type 3).
They are different beads for me.

It means type 1) is a kind of mass production
and type 3) is a kind of "taking a time" production in bird beads case.

I have seen and dealled with so many authentic bird beads and
every bird beads makes me to think so.
(Offcause I know about good fakes as well.Bassam knows.)

In almost case that kind of beads are supposed to be burial accessories.
I believe that type 3) were carefully made (by "carving" or "fusing"..I don't know) for people in higher status than people of type 1).

Blonz duck is famous in the area.
They are popular,so many fakes exist also.
As you know many Blonz are being found in the area and they are called
for "Dong Son" there. And Java people call blonz bird "Dong son" also.
But as you pointed "Dong Son" was several hundred years before the glass beads were made in Java.

So if blonz duck(and other blonz products) were made in same culture in same age as glass beads in Java, it means that so-called "Don son" blonz product in Java were made several hundred years after real "Don son" in vietnum.
Many dealler there point that many blonz product are being found with glass beads.
As far I have no idea about it.

How many times have you visited there?
2 times, 3 times were not enough for my case.
I'm not a good hunter, I just visited there many times( I don't remember how many times....maby around 20 times in this 10 years since I started this business...)
I think it takes a long time( or need big lucky ) to get enough samples in any case.

Oh!There is one more I have to add.
I have visited digging place but I didn't have a chance to see how they are digged up.
In the book "Manik Manik di Indonesia"
they refer to it.
There are some cases.
Sometimes they are being found in a terra cotta pot.
And some deallers there say same thing.

Best

Shinji