"He who marches out of step hears another drum." ~ Ken Kesey
there are thread markers, those are the only thing I trust...but they don't work on poly usually.
You have fixed nothing. Only patched the problem until it walks out your door. The sharpie will fade really quickly and you will be back in the same boat. Plus you will get the added bonus of being the guy that is known for doing it wrong and providing a half a$$ed fix that wont last. Your competitors will thank you for that.The embroiderer should make it right and redo them. Thats what we would do if that mistake happened.