So you're saying Vietnam can and allows to deliberately draw the islands close to her shore but China has to put her possessions within a set space of a map even if the space is not large enough for a larger scaled map because the islands were far and apart. Even a scaled insert would take up a large space. The map certainly was drawn by some foreigners and approved by some northern mandarins that had no knowledge of the south. There are all kind of possibilities and if one use that as proof of non sovereignty is a little absurd.
But anyway the insert on the Vietnam map looks copy-paste to me because I can clear see those parallel line directly under the insert. If you look at the Chinese map the insert for her NW territories is clear and distinct.
You should not blame for insufficient size's paper or lack of understanding of Chinese dynasties at the time, simply they did not draw Paracels and Spratlys on the map of China 1904 that is because the two archipelagos did not belong to China, they belong to Vietnam.
"Đại Nam Nhất Thống Toàn Đồ 1834" [大南一統全圖] (Map of Vietnam 1834) is an old paper map, which is holding by Vietnam's government. The images here are just the photos of its. I dont understand what the hell you said "copy-paste"?
Well, it is true that in 1904 Qing government wasn't in pocession of those islands since they are administrated by someone else, and guess what it was not Vietnam. That is right because Vietname was not even an independent country at that time.
Whether Vietnam was an independent nation or was dominated by France, two archipelagoes of Pacaels and Spratlys have always been controlled by the Vietnamese feudal state and later the French that based on the inheritance of colonial Vietnam.
Remember that before entire Vietnam fell to the French hands, Vietnamese feudal state had controlled the islands for hundreds of years earlier.
When France took over the two archipelagoes as parts of colonial Vietnam, French built the meteorological observation stations, the observatory stations on Phú Lâm (Woody) Island of the Paracel Islands and Ba Bình (Itu Aba) Island of the Spratly Islands, where today are occupied illegally by China and Taiwan.