So, I became what I call a "Blue Collar" fly angler! I've had no reservations about fishing for any species with a fly, and even some that folks, those many years ago, considered "trash" fish! My list of desirable fly rod targets, and certainly because of attitude changes, many other folks as well, have included such species as Carp, Suckers, and various types of Catfish, all in addition to the many panfish species & bass found in my local waters.
Back when I was a kid, my first tying attempts were of flies I saw in magazines, and were mainly trout flies. Again, as I grew up, and my interest in other fish peaked, I started to tie flies more suited to these other species. The problem with this was I had very limited financial resources, and the only available sources for tying materials, was mail order supply houses. So, I improvised!
I've been improvising even since! Much of the materials & even hooks sold for tying, are still geared towards trout. Fortunately, over time many other folks became interested in fly fishing for bass, and saltwater species, but this was not always the case. Today, there are specialty hooks & materials well suited for the larger flies used. There are also many new fly designs that can be used for multiple species, as such, even some of the bigger trout, Salmon & Steelhead flies work well for bass!
I make few differentiations between the various fly types as species specific, except when discussing them with others. This is because not everyone fishes for multiple species or the fishes I'll seek, and flies are generally identified by a species they may have been designed to entice.
It really doesn't matter what the fly was intended to be used for, it only matters that the target species at the time will eat it!