Apple watch serial number

So every watch has own serial number that I understood from your reply.

Last week I left my watch(series 6 nike) to apple store service because I realized some deformations on panel under the screen. And also when I was cleaning the screen with cleaning cloth I was hearing some noises like crunch, actually as if the screen didn't fit on the case.

Apple service approved that and decided to change watch with new one.

I got new watch today, but it is interesting point I realized that when you touch the screen there is still noises like crunch.

After that I checked serial number and it is same with the old one.

If they changed the watch is it possible to have same serial number or it wasn't changed just repaired?

Thank you so much for your replies. This was really helpful.

I will call tomorrow apple service and ask for it.