I've been having a debate about this, so I thought the best place to get feedback would be here.
Do you consider Sister to be an alternative rock album?
My opinion is that the term "alternative rock" wasn't used until early in the 1990's -- particularly after Nirvana expolded -- so claiming that an album released in '87 is "alt rock" is just lazy.
SST wasn't an 'alt rock label' -- it was a hardcore label. If you have to label Sister as anything, why not label it as hardcore, or post-hardcore? Or even 'indie', which is what a lot of people called Sonic Youth-like music, until "indie" became synonymous with British major label pop in the mid 90's.
Sister definitely helped define what would become alt. rock in the 1990's, but claiming it's alt. rock is like claiming The VU & Nico is 'punk rock'.
This is probably not the most interesting debate ever, but never mind
(or Nevermind?)