I would hazard a guess that if someone has a severe nut allergy 9/10 we won't hear about it as crew, or if we do hear it's normally because we go to serve nuts to pax seated next to them, they then decide to speak up once the whole aircraft is eating...
I remember flying with a senior once who insisted we read the labels of every product and didn't serve even those with traces of nuts. We could hardly give out any food under that ridiculous policy, the end result of one pretty annoyed bunch of pax.