It's impossible to determine whether a value from get_figma_data is a computed 'auto' value or a value that was actually set by a designer.
For example, for a frame that has no gap property set in Figma Dev Mode, get_figma_data still returns gap: 18px.
For frames where the gap property is explicitly set, the function returns the correct value as expected. This leads me to believe I am observing this correctly.