There may be certain nutrients present in trace amounts in a product. For one or two consumption, these trace amounts might not be dangerous, but consumption of the product over extended periods may lead to health issues. That cookie just might not REALLY be devoid of trans-fats, its just devoid of sufficient trans-fats that the manufacturer does not need to declare it.

I can’t recall the exact quantity, but the FDA does not require that all nutritional data are fully listed, if the quantity falls below a certain threshold, manufacturers are not required to actually list it. I’m not sure whats the case for Singapore’s declaration.