Have I got the calculations right?
Yes, that makes sense, although Tesla still says 2.3kW when you are saying 2.07kWThe calculations are correct, but some of your assumptions are optimistic.
Although a "13A" plug, experience dictates that they aren't suited to continuous operation at that current, and manufacturers of EVSE (including Tesla with the UMC) have adopted 10A as the safe limit.
The NEDC range is hopelessly optimistic and no use for practical purposes. On the other hand, you are assuming that a "75" has 75kWh of usable battery, when in fact a portion of that capacity isn't available for use, so your "realistic" calculation is actually pessimistic. I use 333Wh/mile (or 3 miles per kWh) as a rule of thumb - it's an easy figure to work with, and actually matches very closely to my lifetime average shown in the car. I have the displays in the car set to "typical" rather than "Rated"(=NEDC), and I believe the "typical" calculation uses a slightly lower figure, about 300.
There is an overhead on charging - a (quite small) percentage overhead on the power conversion, but also a fixed overhead for running all the computers/cooling systems/etc that have to be powered up to enable any kind of charging. As a round number, deducting 1A for this (230W) is about right.
Actual current drawn from 13A socket: 10A
Deduct 1A for fixed overhead: 9A
Convert to watts at 230V: 9 * 230 = 2070W
Convert to MPH at 333Wh/mile = 2070/333 = 6.2MPH
Convert to MPH at 300Wh/mile = 6.9MPH
Tesla still says 2.3kW when you are saying 2.07kW