That's the thing.
A constraint not specified - does not mean not meant.
Instigator gets like arrested: "everything you say may be used against you in court".
You've got to right your requirements similar to EULA from MS or Apple, or, better, both of them combined.
Otherwise the creative team will find their way around and you'll end up with a granny instead of a fruit.
And 3 years into the project - the the job of the PM from the side of the instigator is very much doomed no matter what action he/she takes in this situation.
Unless he/she is also creative enough to convince the board that the granny was actually what they needed from the very beginning.