You can usually find drivers older than August 2016 that get trained and suddenly jump 3 levels.
Kevin, I think you can understand this because there used to be attributes in old iGP that drivers don't have anymore. Things like Charisma and Work Rate and Wet Weather ratings.
These attributes diluted the length of time it'd take to level up a driver. When these were removed, the dilution was reduced greatly. So the moment any one of the existing attributes was increased by +1, the driver instantly goes up 3 levels.
The issue lies in that these old drivers' levels are misrepresented until they are trained.