Alice invents a widget, files patent; it gets granted after a couple of years. Meanwhile, Bob has copied the widget and been selling many units of his copy.
Alice and Bob reach a license agreement whereby the latter will pay the former a royalty per unit sold.
By law and custom, are back royalties due back to the date the patent was filed? Or do they only apply forward from when the patent was granted?
And have the rules for this been the same since the patent system started, or have they changed over the years?
The jurisdiction I'm concerned about is the US, if it makes a difference.