Alt rock can be used to describe thousands of bands, modem and vintage. Going to need to be more specific
I think OP is loosely defining "alternative" as music influenced by the early 90s rock and roll phenomenon which replaced Hair Metal in terms of popularity. This music did not come out of the thin air, but rather was influenced by the many independent, underground, and post-punk bands that existed in the 1980s.
However, Alternative is a wholly manufactured and prefabricated musical style that was developed as soon as eMpTyV and the recording industry figured out how to make a quick buck. Real alternative bands remained on independent labels while others went platinum. This nom de plume of "Alternative" is deceiving in and of itself; musically speaking, Nickelback is alternative, but you'd be hard-pressed to convince anyone they are anything but mainstream.
Also, there may be the grunge elephant in the room, so we'll address that as well. Grunge did not exist. It was merely a bunch of metal and punk bands from one local scene that all got signed all at once.
While we're on the subject of Seattle, two other local scenes were also similarly exploited although to a lesser degree during the whole alternative craze: Boston & Chicago.
Still don't believe alternative never existed? Look at Emo. Based on post-hardcore punk it became a bloated shadow of its former self. The recording industry tried to do to Omaha, Nebraska what it did to Seattle but it did not succeed.
I probably sound like a curmudgeon, but using the term "alternative" to define a club is just like people going out and buying Les Pauls to play blues or the Dimebag Darrel guitars to play metal. The music is in you, not the instrument. If you sound like crap, it doesn't matter what you play.
