...That, uh. Might take some explaining.
See, every band has a unique signature that allows you to identify it as them. Even similar bands sharing key members. (For instance, Death Cab For Cutie has a distinctly different signature from Postal Service. I happen to suck at guessing which is which because while the difference is there, my personal ability to distinguish between similar signatures sucks. I can do it in theory, but without looking up the song online for absolute confirmation, with me only knowing their songs via the radio, and only having limited exposure to them, it's basically just my natural ability, which is...high enough to know there's a difference, but low enough where I'm doing nothing but a best guess.)
Said signature, of course, is just like a real-life person's signature over the years: it can change with time, members, albums, and even recordings (i.e., live vs. studio), which is why I didn't rule out Offspring--because it could have been a live recording during a time period where I hadn't heard their norm rendering their signature hidden, there was the possibility (albeit improbability) that it was them. Yet the more I listened, the more I doubted it was them.
I did briefly consider Rise Against as an option (Rise Against having some vague similarity in their signature to certain periods of Offspring music), but having heard End Sessions from them, knowing their sound doesn't change as much as most bands, and having a fair idea of their signature being different, I ruled it even less likely than Offspring. I quickly shot through other options, running the gauntlet from Killers (instantly ruled "no"; don't know why it even crossed my mind), Modest Mouse, Franz Ferdinand, and then, I had a breakthrough.
From the moment the song began, it sounded familiar, even though I didn't recognize it. Running through the bands and songs of theirs that I knew, though, eventually led me to listen closely enough to find why it was familiar: there was a very notable resemblance to both An Honest Mistake and Believe. (Different parts of both.) In other words...a third Bravery song I'd never heard before that moment, but still recognized as being theirs.
Makes sense, of course, because I loved the song. I love the Bravery songs so much, memorizing their lyrics as much as I can, relying on them, listening to each aspect of the music, that it made perfect sense for a song I was loving that I vaguely recognized yet didn't know, for it to be them. By finding their signature, I identified it. Of course, I didn't know for sure, just having it as my theory, but my coworker later confirmed my suspicion. Felt good.