No matter how many different formats/sizes you download an icon in, it still counts as one download if it's the same style.
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To clarify, each unique icon counts as one download. Each icon is assigned a unique ID which can be found in the icon's link address. If you download the same icon in different formats, sizes, or colors (but not styles), it will still only count as one download.

Please note that downloading the same icon in different styles will count as separate downloads since they have different IDs.