That's very possible. However, looking at 3rd party site that lists ingredients and nutritional information, Jiffy Corn Muffin Mix did not contain partially hydrogenated vegetable oils and listed zero grams of trans fats [0]. The site doesn't list when the information was added but the comment history goes back to 2011.

They do also have a page for a Jiffy Baking Mix (no corn, sounds similar to Bisquick) that did contain partially hydrogenated vegetable oils, enough for one gram trans fats per serving.

[0] https://www.fooducate.com/app#!page=product&id=43DBDE62-E10F...

[1] https://www.fooducate.com/app#!page=product&id=43BFE144-E10F...