BLA BLA BLA etc to remove the ECU in the workshop manual but who would have guessed you need to change the oil and filter

All vehicles
To install, reverse the removal procedure.1.
Vehicles with diesel particulate filter (DPF)
Renew the engine oil and filter.
 FL2 MY10 TD4 GS traded in at 2 years
FL2 MY13 TD4 GS Current

what, why.......... Common sense isn't very common.
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2007 Land Rover Freelander2 I6 hse Auto

Pretty sure those with DPF have oil condition monitors. Perhaps when changing the ECU it needs to know that the oil is in A1 condition as a starting point for monitoring purposes? Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.

I am sure you are right with your view Steve but it would be so easy to miss when it was being changed unless you had read it up. One to remember.

Now what month is it ?  FL2 MY10 TD4 GS traded in at 2 years
FL2 MY13 TD4 GS Current

The procedure of changing an ECU implies clearing and initializing some information inside the ECU. Among those the oil quality.
If you don't change the oil, then the oil quality will be out of sync with the oil quality information stored inside the ECU.
You will have an used/old oil in the engine, but inside ECU will be considered as new because of that ECU initialization.

What a good guess from me in the first place.  Past: FL2 TD4 HSE Auto
Evoque SD4 Dynamic Lux Auto
Present: Audi A3 S Line.