I've seen them without the markings on the el's. On this model only. Like 2015ish ones. I think they are just marking them on the clasp and arrows on the removable links... maybe the # is on the inside towards watch?
ON the watch there is a factory seal of red color.
Omega used to put the red seal on the caseback from the factory. If still intact, it means the caseback hasn't been opened since new. This also means the watch hasn't had a service since new.