Regarding the UK allocation statement, this may be a short term reason due to the pandemic, Gordon, but in normal times, your order will generally be factory built, unless there happens to be one in your spec available.
This may differ slightly for models like the GLA Urban Edition which have a set spec with no options. In this case, cars can be diverted from a dealer in a country to other dealers in another country with a requirement if caught before shipping.
? I will be remembered for nothing but had great fun doing it ?