Be aware that if a small change is made to an aircraft, like adding or removing equipment, the airplane is typically not reweighed but it's empty weight is recalculated by adding or subtracting the weight change. Also, the empty weight c.g. is recalculated by adding or subtracting the moment change.
As I remember, there is also an requirement that aircraft be reweighed every so many years. I want to say every 3 years, but that may be wrong.
Also, the empty weight does not include pilots and cabin crew. The term BOW (Basic Operating Weight) is often used that does include standard weights for pilots and cabin crew.
Air carriers, particularly freight operators, may employ more than one BOW to allow them to easily switch between configurations. For example, freighters sometimes carry fly-away-kits (FAK) of several hundred pounds. The kits are strapped down, but can be quickly removed if need be. The operator might choose to have two BOWs, one including the FAK and one without it.
There's also the matter of using "fleet weights" rather than individual airplane weights, or at least there used to be.