I personally don't expose the choir to the song until after I have finished teaching it. As the director, I like to have the control over how the song taught to them. Of course nothing is to stop them from going out and researching and finding the song for themselves, but as a whole, i'll teach it first.
And even then, i don't send out CD's, but rather I have a webpage that I have the songs posted and the choir members can simply go to the webpage and play the song directly from the browser. I have the artist/track information on there, and even make the mp3 available for them to download if they choose, but i gave up burning cd's a long time ago, it got rather time consuming and expensive.
My members love the format, they don't have to worry about keeping track of cd's.
But to answer the question at hand, I don't give them the song until AFTER it has been taught. I try to teach every song according to how it was recorded, but if by chance I do get a note or two off, i want us to ALL be off together, and not be arguing with a tenor because he thinks the note should be different than what I showed.
Just my 2 cents....
Tj