Templates and Duplicate Masters

I've created a template with 13 slides that I'm using across several courses. The 13 slides share two different slide masters that have several layouts each.

My issue is that with each slide template I add to my project, even ones previously used, a new copy of the slide's master is added to my file. Unfortunately I didn't realize this until later on in one project and ended up with 25+ copies of the same master. Not fun when you have to make a change on a master...

Is there any way to prevent all of these duplicate masters from being created?

The only solution I've been able to think of is to add all template slides to my project file from the beginning into a single scene, then use these as my templates, making copies of the slides as I go. I can't think of a major downside to this but it seems like an unnecessary workaround. I'm posting my question anyway should there be a better solution someone might be able to share with me.

Thanks!