Don't remember where I read the story or which movie it was where a pair of sun glasses was written in one scene and, if I remember correctly, there was a quantity of them made and several shoots where different pairs of the same sunglasses were used and I think the bottom line in the story was that all of the pairs of the total amount used as props and/or spares had the same value since it would be virtually impossible to pinpoint which set(s) were on film. I may not have it all right, but it was an interesing account of the number of the same prop was on location.