A unique product (SKU) is an item appearing in the system for the first time and has never been processed from any client before.
You can upload any number of feeds, including from different suppliers. If the system detects items that have never appeared before, they count as unique products.
Example: if you upload 5 feeds of 1,000 products each, but the system finds only 3,000 new unique items in total (considering duplicates), only these 3,000 will be counted.
Unique product tracking is done at the system level, not just within your account.