Master no longer copying

I created a master that I want used for all our content. For new courses, we just start with the project and Save As. However, for existing courses, we were able to copy one slide over and it transfer the new masters for us to update the layout of the older content. This was working fine for about 6 months, now some components of the new master will not transfer over. How do I get the new master slides into the existing courses?

Thanks.