By the end of the 19th Century, so many countries had issued silver world crowns that I generally need to focus on selecting just one example per country for my custom set, that I have playfully named "My World Crown Affair". Chief among my criteria is that the coin was minted in the country. If not locally minted, then a design element should be strongly representative of the country. Quite a few examples of coins issued for colonies lack any flavor of the local culture and thus fail to interest me. An additional selection preference is that when issued, the country was independent. This last criteria can be a serious constraint for countries that issued silver crowns during brief periods of independence.
The country that we commonly refer to as Vietnam has had many official and unofficial names. In the early 19th Century the independent empire of the Nguyen dynasty was called "Nam Viet", "Viet Nam" and "Dai Nam". Increasing French influence undermined the empire's independence and after 1845 the name "Annam" was used for the French protectorate followed by "French Indochina" when the French consolidated their rule in 1887. I have seen catalog descriptions of coins issued during the period of independence listed as coins of Annam. While it may be convenient for a catalog to broadly group issues together under one name I consider this, at best, misinformed; at worst, downright disrespectful.
Dragon Dollars or Silver Dragons are names for the Asian silver dollar sized coins issued in China and Japan at the end of the 19th Century in emulation of the Spanish Colonial and Mexican 8 reales that were the dominant trade coin. But the first of these silver coins with a prominent dragon design was actually issued by Emperor Minh Mang of Viet Nam. The earliest of these are undated and the first dated coins show the number 13 indicating the regnal year, 1832. The specific denomination that corresponds to the 8 reales trade standard is the 7 tien, weighing almost 27 grams. The casting of coins in East and Southeast Asia had been established since ancient times and some opinions that you may find on the internet claim that the silver issues of Minh Mang and subsequent rulers were also cast. Fortunately, there are more informed resources to consult. The Standard Catalog of World Coins lists these as milled as do many of the top auction house catalogs. And a few of the finest examples are encapsulated in mint state grades by TPGs indicating that the coin surfaces still exhibit the luster that occurs from the metal flow when a planchet is struck. If you examine enough good photos of these you can notice some instances where the planchet was not perfectly centered -- a feature of a coin struck in a open collar press.
My example is from the 14 regnal year, 1833, shown in Chinese characters beneath the dragon, the obverse shows the characters for Minh Mang and Thong Bao (general currency). It exhibits circulation wear and environmental damage in addition to the holes where it was likely used as a garment adornment. Having examined many 8 reales of the contemporary time I am comfortable with the assessment that this is a milled/struck coin just from the appearance of the surfaces. Devices are sharply defined, there could be a die crack and there may be a bit of toning shadow that is sometimes seen next to a device but always toward the rim where the stress from metal flow alters the way the surface forms its patina. Ultimately, the examination of the edge provides the necessary proof. My photos of the edge clearly show that the coin was run through a single die edging mill (a parallel edging mill would show a second gap opposite the one gap in the oblique reeding) and you can see from the uneven profile that the coin was probably edged after it was struck (otherwise the flat surfaces of the coin press would have provided a more even profile). Both the dentils on the rims and edge designs were features added to milled coins to make them harder to counterfeit and to clearly show if any slivers had been shaved off. Of course, my example may be atypical or even a counterfeit. However, it was purchased through the Stephen Album auction house and came with a provenance. It's just unfortunate that you never get to see the edge of coins unless you can examine an unencapsulated example in-hand. I should add that the Standard Catalog of World Coins notes that there is a variety of presentation pieces without milled edges.
*I apologize for omitting diacritics but you just can't be sure everyone's browser can display them properly.