Is the number in the Apple Watch Ultra strap slot it’s serial number?

Thanks Niel, looked at another photo of another watch & I can see the serial - to the left of the slot. Wasn’t visible on the other photos I’d been sent.

……& is there a number in both sides? Just I’m trying to find out if a used watch is genuine & I was sent 2 photos of two watches with the same number - which isn’t recognised by Apple? (The number is EN13319)