Lots of good advice above. If you look for a "definitive" version of a song you'll usually find at least a dozen, so don't worry too much about getting the correct version. I recently heard a song I liked, bought the CD from the composer and learned it, only to hear him sing it in an amended version a few months later - he hadn't been happy with his first version. In any case, even if you learn a particular version, you'll almost certainly deliver it differently on different occasions. Sometimes I feel a song wants to go a different way from the way I'd planned. Hope that doesn't sound ridiculous; it's a fact. Best of luck with the career.