Hi there,
if the Two Content Templates have the same Display Rules then yes you will get duplicated content.
Choices:
1. Ensure that each Block Element Content Template have different Display Rules.
This will allow you to have one type of post layout for your Blog and a separate layout for your Category Archives for example.
OR
2. You can use a Parent Block to mix and match different templates.
a. Create the Global Template and set the Apply to: All Posts. Set the Display Rules for Blog and all your Archives.
2. Create a Category Specific Template and set the Apply to: Posts with Term ( select your taxonomy ). Below this you will see an option to Select: Parent Element. Change this to the Global Template. In doing so it will remove the Display Rules from this element – as it will use the ones set in the Global Template… but you won’t have to think about exclusions anymore.
What this will do is apply your category specific template to only the posts with those terms, and all other posts will display the global template.
You can add as many term specific templates and assign them to the same Parent.