Well done! I didn’t knew there were that many differences between all the artworks of Gyarados. When I was working on my National Index collection including all forms and shiny Pokémon I was including minor artwork differences as well (see “Unofficial / Artwork Errors” sections), but apparently there are a lot more when you take a much closer look. 
Btw, the color of the whiskers of Gyarados is actually another one that’s different for the Base Set. Male Gyarados have blue whiskers (which is true for almost all TCG cards); female have white whiskers (there aren’t any TCG artworks of Gyrados with white whiskers*†*); but the Base Set artwork has light red whiskers.
†: Male Magikarp have yellow whiskers and female Magikarp have white whiskers, so the Base Set Magikarp is female, and every other Magikarp TCG artwork is male. 
Greetz,
Quuador