X has no business knowing what Y makes. And if you are so open with your employees, you wouldn't wait until X asks. You would at least on an annual basis, during annual reviews, explain the employee's strengths, weaknesses, areas to target for improvement and set goals for growth, both professionally and for compensation. X still isn't entitled to know what Y makes.
“X still isn’t entitled to know what Y makes. “
I’m not saying they are entitled, legally or otherwise.
You can run your company any way you damn well please.