I've been developing a software for 4 year, and I have spread parts of it under a GPL license for 2 years without being aware of it (it's complicated) since the beginning of the project.
I built it in partnership with a foundation, which put money on this, at the condition to put it under GPL : I've seen the contract made between my company (which is a public school) and the foundation few months ago.
I've built a significant number of things upon this GPL version since, without knowing it was going to be GPL too, and was about to use it for commercial purpose.
Is there any way to use dual licensing on that case, in USA ?
Disclaimer : I'm in France, so if there's any french folks around, I'm more interested about the french law ; just replace GPL with CeCILL_v1 (GPL equivalent in France).