Are all dark chocolates with the same amount of cocoa equal? I've noticed 3 ingredients in all dark chocolates:


cocoa mass
cocoa butter
cocoa powder.


This made me wonder if someone could have different ratios of these ingredients (like more cocoa powder than cocoa mass) and still have "dark" chocolate with X% of cocoa while being inferior to some other chocolate.

Another thing I've noticed is that many chocolates have approximately the same mass and amount of cocoa while having very different amounts of sugar (from 15g to 45g), if they have approximate amount of cocoa and mass, how did they stuff additional sugar in it?
There's just a ton of different types of dark chocolates out there that cater to all kinds of needs:


Chocolatiers
Bakers
Gourmets
...


To answer your questions: 

Yes, it's rather easy to have a "more fluid" dark chocolate that still contains a high % of pure cocoa and cocoa mass by adding more cocoa butter.

Cocoa mass is a raw ingredient that comes straight out of the beans and cocoa powder and cocoa butter are the separated products from cocoa mass, so to add more sugar, Chocolate producers use the same amount of cocoa mass and powder but a bit less cocoa butter.

One additional factor to consider is the chocolate bean roast and quality. Like coffee, the roasting process can affect the taste.