Not all paintings signed by him may have been painted by him. A friend told me that a painter friend of his invited him to go visit Dali. My friend chickened out and regrets that he did. He just waited on the street while his friend visited. His friend went in with his paintings. Later came out with some of the paintings with Dali's signature on them. Back in those days painters would sell their art on street corners and if Dali liked the art,he'd sign it.
Don't know how much of this is true but my friend is not one to make up stories. The way he says he regrets not meeting Dali makes me believe him...yet I find it hard to believe.
There are stories that as Dali’s mental status declined in later years, he would sign blank canvases and hand them out to visitors. As a result, more recent Dali specimens are highly suspected to be forgeries.