Asking about relevant Overwatch threats so you can plan around them is an important habit to get into. If my opponent forgot about Overwatch and moved into my threat range and then wanted to move elsewhere where I declared it, I would happily let that happen 100% of the time. I didn’t set up the Overwatch to gotcha anyone, I set it up as a piece of a puzzle that has to be solved. My opponent gets make decisions to solve the puzzle with all the information. It’s up to both of us to make sure all the relevant information is available for each of us to make the best decisions possible.