While
The Difference Engine did seem kind of unusual when I read it back then, I never imagined it solidifying the once scattered and isolated instances of pseudo-Victorian speculative fiction into a sustained momentum. Of course, it's no longer even referenced as what triggered the coining of "steampunk", since K.W. Jeter did that directly a few years prior. But I guess it's still tooted as what officially broke the dam and got the movement flooding and recognized on an international scale.
One problem with the punk-genres having that shared word-unit is the indignity of them simply being tongue-in-cheek spinoffs from the original "cyberpunk", which in turn was borrowed from the music culture of that late '70s, early '80s era. The definition of "punk" needs to be refined deeper or generalized further to reflect the later developing usages. Thankfully that has been done:
Piecraft: Perhaps it is best to accept that the 'punk' suffix added to these literary genres developed not out of the same sense as the punk musical scene, but out of the actual definition of the term. Punk referred to a label given to antagonize anyone who was seen as rebellious or anti-establishment; mostly designated to the younger generation, basically one who would go against the grain of society.
This 'punk' attitude was further enhanced with cyberpunk in an all too bleak view of the 1980s drowned in the Digital Age and mass consumerism, but it was later carried into the extraordinary adventures and inventions found in a curious age before the turn-of-the-century. An age that reveled in the world of steampunk, with high hopes about industry and progress, bringing about exciting technology but also social change. Thus the daring adventurers and anti-social inventors of this time could be seen as the 'punks' of their period, rejecting the status quo of the time to challenge and seek their true destinies. We observe that this was further enhanced by the inclusion of the urban, gritty and raw characters found in the 1930s, demonstrated through film noir and pulp literature. --
The History of Dieselpunk III: Diesel’s Punk
Larry Amyett, Jr: [...] the number of proposed genre-punks has multiplied faster than wildflowers after a spring rain shower, three genre-punks dominate this phenomenon: Dieselpunk, Steampunk and Cyberpunk. --
The Genre-Punk Linguistic Family Tree