The ESP Guitar Company

Does anyone know how the production number (4 digit code) is assigned for recent years.  Example, I’ve seen ESP Original Horizon’s with production numbers ranging from about 1600 to over 9000 within the 2019 year. I know they didn’t produce that many so the numbers likely aren’t consecutive. Any idea how they’re assigned? Again, this is just a question on the production number and not decoding the whole serial number which is already established. Thanks.