We only count active SKU's for billing/inventory limits. This means we only count items(SKU's) with a quantity greater than 0 that are active in a marketplace. You may have some inactive items in your inventory with quantities; these do not count towards your inventory limits because they are not listed in a marketplace.
For SKU's that are shared(cross sold) on multiple marketplaces, they only count as one for our purposes.
Example: Selling a bowl, SKU 1234 on eBay, Amazon and Shopify. This SKU only counts as one, because it's the exact same SKU in all marketplaces.