Data can come from many points in the chain.
Energy into the motor? -> traction only, not accounting climate and accessaries.
Energy from the battery when driving? -> not accounting for when car is parked. (Tesla counts this)
All energy from the battery? (such as vampire drain, pre-conditioning usage, sentry mode usage)
All energy goes into the battery?
Energy delivered at dispenser unit? How is the car going to know about losses between battery input and dispenser unit?
Energy went through the meter, with transmission losses before the charge point?
Electricity is very efficient in everything (eg. heating, LED lighting, battery storage, inverter/rectifier, transmission) , but there are many small percentage losses everywhere. At some point, a decision must be made on where to measure.
I personally don't see any problem only measuring battery consumption during driving. Remembering electricity is priced at 7.5p/kWh for well over 90% of my EV charging. 😜
Today, I drove into London, parked up about 10min walk from Buckingham Palace, a street away from St James' Palace for £1.34 (Westminster 10min parking fee for EV's, max stay 4 hours). This 20 odd miles trip would cost ~60p in electricity at most. No congestion charge, Might as well get most out of parking discounts before it goes away.