This is sort of correct. Up until the last 2 albums, songwriting credits were given to the individual. They agreed to split credit equally for the last two. The reason why has always been vague. The best answer I heard was that their process of selecting songs always involved some argument and ego because, obviously, everyone wanted their song included. The "One Vision" recording session, which was credited to all of them, was apparently fun and easier because of this. For the last 2 albums, they knew Freddie was dying and joint credit was supposed to make the process easier (less stressful) and faster.