I would love to engage a discussion about dating aborigine’s items. It seems always to be a sensitive subject.
For example, I would kindly disagree with our host about the #Am 401 and 402 which could be from or before the thirties (as the book: Glass-plates images, Collected material of the department of Anthropology show some amis people wearing these clothes) On the other end, to my experience Am 506 could also last from the thirties to the fifties; the type changed in the sixties and become much more "barock".
For the amis, the evolution in clothing is following the Han clothing in a funny way.
But this is not my point.
Most of the time, the determination of date could be done following the kind of colours and fabric, which has been used. By example, concerning the atayal clothes, the red colour is changing from the natural dye to the industrial and then artificial colours, giving different hues and values, following the periods of time, before and after the turn of the century.
On reproductions, prints or web sites, it is difficult to figure out which colour it is.
I would be interested to know more about the real colours of the atayal clothes: AT 0301, 302, 403, 404 etc
Beyond dating, it is fascinating the see the adaptations of all people to the evolution (fabrics and dye) provided by the Japanese occupation.

Hi Victor
Welcome on board. Glad to see you here !
This a very interesting subject. How to date the items ?
Personnally, I use different ways and then after comparing the results, I come to a date that appears reasonable but should be quite conservative.
First, I check the material used, knowing that old material is not a guarantee of age. In the fake made to deceive, old material can be used or reused today, or new material can be made to look like old.  Another way to be mistaken, is that the material used can be authentic but coming from another culture and used to deceive the collector of Taiwanese aboriginal items.
Second, the technics and the tools used. There are always ways to see if the objects or the clothes are handmade or not, what kind of tools have been used, traditional or mechanical, to make them.
Third, the information I have. I always look for similar items in the documentation I have, mostly books, but it can also be artifacts exhibited in museums or seen in other collections. Having informations on the origin and provenance coming from the previous sellers/owners is another very important way. Then, looking at the other items coming from the same lot gives me also a great deal of infos.
Fourth, my caution and my experience as a collector usually dictate me to date the object/cloth with conservatism and, most of the time, to choose the latest date.
To answer precisely to Victor :
#Am 401 and 402 : I used book/pictures references and also checked on the fabric, the buttons, the way it was sewn… I have to say that I relied also on the infos provided by the seller and the fact that these clothes were included in a lot, with many other clothes that were all from the same origin and mostly from the same time. This fact helped me corroborate my initial evaluation for the datation. All this lot was coming from a missionary stationed on the eastern coast of Taiwan in the early fifties. Let’s say that these items could be from the 40s or even the 30s, but I preferred to be cautious.
AM0506 This one could from the 50s but definitely not the 60s. What convinced me to date it as made in the 40s was that I checked the material and it appeared to me as dating from Japanese time, not the Chinese Republic time, even if it is not an absolute proof because earlier material could have been used also in the 50s. Then I concluded that the handcraft was more looking like something older. I also remembered that I had seen similar items, with the same technic and material, that were made in the 40s. That’s why I chose to date it from the 40s. In the Shungye Museum of Formosan aboriginal art, you will find on p.150 exactly the same collar called shoulder cape. It is made at the same time, with the same material. Unfortunately, the museum is not dating its items.
Gehaobo