We don't know but its on them to explain especially if they don't have anything to hide. Understand though I'm one of those that could care less if Drake wrote one singe line or verse ever. If I can still listen to Rick Ross after what I know about him then I've accepted that music in general is just entertainment.
Drake is more of an R&B singer/entertainer to me than a rapper so my outlook on him isn't shattered if he didn't write some songs or any songs for that matter.
Drake shouldn't be anybody's hero.