When publishing through a schedule you will always publish a placeholder instead of the normal banner tag. The script tag may look the same but the placeholder is a container that will display different banners depending on what is in your schedule apart from the banner tag which will only show the banner that you published. 

How does a placeholder work?

A placeholder is a container which is relative to a combination of a Language and a size. What this means is that the placeholder can only display a banner which is relevant to it's combination. For example, the 300x250 English placeholder will never be able to display e.g 300x250 Swedish or 728x90 English.

What is displayed in the placeholder depends on what banner set(s) concurrently is active in the Schedule timeline. If no banner in the active banner set matches a placeholder, then schedule will try to display a banner of the placeholder based on the backup banner set and if the backup banner set doesn't have a relative banner then the placeholder will display nothing.

Checkout the image below that explains how the placeholders works with a graphic illustration. 

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