Completion is a complex issue. I think a lot of factors go into why someone would complete or not complete. The point is let's take down as many barriers as possible. If it's a barrier because you feel you can't go because it's a really busy time, and you don't want to ask your boss if you can go to technical training.... It could be that the technical training is not being offered, that there aren't enough people in that trade who want that technical training right now. It could be that technical training is taking place at a busy period, versus not a busy period.
So many different factors go into whether or not somebody completes. In some trades the movement is important. You have to understand that some employers might think they'd rather keep a second-year apprentice because she's a good worker and they get to pay her less if she's a second-year apprentice. There are reasons on both sides not to go to technical training and progress.
Alberta has done something whereby if you don't progress within 18 months you are deregistered, which is a motivation for both the employer and the apprentice not to lose their work-hour credit.