Funny thing about that... I usually don't know what the lyrics are to the songs I'm playing. I'm not proud of that fact, and often ask the singer to share with me what they are, but in my experience, they're often reluctant, unwilling, or at least flakey about sharing. My failing has been in not following up.
But in my defense, I don't like rehearsing without vocals. The fact is that I more or less consider the human voice as another instrument - and a really important one. Apart from locking in with the bass player, I'm perhaps most keyed in to the vocal parts. But it doesn't mean that I need to know what the words are, unless there's something there to cue off of.
I played in a band with a singer who was a heroin addict and I didn't have a clue. He had songs about it that, upon hearing the words later, made it quite clear what he was up against. I was pretty embarrassed to have never picked up on his habit having been exposed to his declaration of it every time we played that particular song. (he's been a clean and sober family guy for the last 15 years, FWIW)
Here's a first: The band I've been playing with the last few months has a singer that is more than willing to share her lyrics. She just emailed them all to me earlier today and I didn't even have to ask! Pretty dang cool, if you ask me. Really good lyrics, too (and what a relief!).