Hi there! Welcome to the site! You've asked quite a loaded question here. Lengthy post incoming...
Michael had recorded sporadically between the summer of 2005 and the summer of 2006 -- at least two songs were recorded during his time in Bahrain -- but his first sustained effort at working on a new album took place in September/October 2006 in Ireland with will.i.am. After that he vaulted from location to location without much concern: sometimes he'd be recording in a state-of-the-art recording studio, and sometimes he'd be in a hotel bathroom. He was writing and plotting and planning and conceptualizing up until the days before his passing, but his final vocal sessions took place at the Bel-Air Hotel in Los Angeles, where he recorded "Best of Joy" from Michael, "I Was the Loser," and one other unknown song. Sort of bittersweet that one of the last songs he ever put his voice to included the lyrics "I am forever," isn't it?
Collaborator-wise, Michael was dipping his toes into the current charts while still keeping one hand on his past. He worked most frequently with Brad Buxer, Michael Prince and Neff-U, but also spent some time in the studio with will.i.am, Akon and RedOne. Sadly, Michael died before several of his planned collaborations could happen: Ne-Yo submitted some demos but nothing was ever recorded; Michael held various meetings with T-Pain, Kanye West and StarGate to discuss working together; Swizz Beats was apparently working on some stuff; and Rodney Jerkins, Dr. Freeze, John Barnes, Bill Bottrell, Cory Rooney, Rod Temperton and Teddy Riley all either met up with Michael or spoke to him on the phone about hitting the studio again.
In terms of the material he was working on, Michael had always been keen to revisit old material that was never released and update it for modern times, but he seemed immensely nostalgic during his final years. At least half of the titles known to have crossed his path from 2006-09 were recorded during or prior to the Invincible sessions. I believe one or two of them were even traced back to the late '70s/early '80s! There was new material as well, but he seemed particularly focused on reviving older music, including songs that had already been released ("The Way You Love Me," "Beautiful Girl," "Cheater," "Scared of the Moon").
As far as completion is concerned, no one really knows. It's been said that most of the material, particularly anything written post-2006, has scratch vocals at best. Apparently the leak of "Hold My Hand" hurt Michael to the point where he refused to put vocals down until he was truly ready; he knew that an instrumental had little to no no value. Some of the titles we know of have been said to have full vocals, while others don't; it's sort of a guessing game until someone can come along and confirm it for us. However, RedOne has stated that he has enough to put together a few songs, while will.i.am is sitting on at least three finished songs, including a James Brown tribute. God knows if we'll ever hear those songs though: RedOne said he'd only put them out if the proceeds went to charity, and will.i.am has flip-flopped on his stance over the years.
That's the gist of it!
