The GPL3 defines correspond source as the following:

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> The “Corresponding Source” for a work in object code form means all the source code needed to generate, install, and (for an executable work) run the object code and to modify the work, including scripts to control those activities.
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What does it mean by "source code needed to ... run the object code"? Is this solely in reference to dynamically linked libraries, as mentioned later in the paragraph, or does this also include data files?

I should note that this is a practical issue since fonts and images are often licensed under free licenses incompatible with GPL (OFL, CC BY SA 3.0, etc.)