yes, and the exact meaning of definition of made or assembled in any given country might vary enormously and might not be meaning the same for different products.
While the definition of Made in USA is very well regulated, it is , for example ONLY compulsory for automobiles and textile, wool, and fur products.
There is no law in USA which makes compulsory to label anything else, but if one does label it as such, it has to be true (in as much as the law applies to define what’s made or assembled).
In Japan, things can be even more complicated. The definition of “ country of origin” extends to the country where the assembly has been made and there are different proportions depending on the type of product of actual Japanese product that might have to be part of the assembly or not.
So, it is probably allowed ( I don’t know) to buy taiwanese parts, assemble them (the level of assembly is, I think but I a m not sure, also not exactly determined so you could, in theory, get a horn where you only have to mount the the palm keys and still qualify under assembly.
This is a phenomenon which is now heavily present in watches and consumer electronics where the actual assembling has reached the point of putting together ,even in a minimal or insignificant way, parts that were mostly made and almost assembled almost completely elsewhere.
It is a jungle out there.
So currently there are many brands all over the world claiming that they make or assemble horns from parts made elsewhere. All implying that their assembly would be thus superior to the one in Taiwan or China or Vietnam (because for all we know parts that are claimed to be made in Taiwan could be made in China or Vietnam).
What I always say is, if you assemble, or claim manufacturing, since this is important to the customer, show it in your advertising material and be overt about it without burying the information under tons of distracting words.