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HankronGlen is correct. While some trade cards were directly related to a particular product, most trade cards were sold to stores or other commercial companies who put their individual stamp on the front and/or back of the card. So, for example, an 1878 Forbes Trade Card (common type, Forbes being the printer of the cards) can be found with a 'Joe's Candy Store,' or 'Tammy's Carpets' on it.
In a sense, many (not all) trade cards were like Christmas cards you buy in a box of 50 at the store. The message part of the Chistmas is left blank so the individual can add her message and name.