Registering is a bit random, it is a manual process for imports I would think.
My guess, but I have only registered 4 or 5 vehicles, if the right word isn’t in the right box then it probably isn’t in some drop down menu. If the person in dvla doesn’t have to fill the box in, then they leave it blank.
If they are having a bad day then they might just return the paperwork.
In your case ? Are you saying the vehicle was modified, say from a 110 to a 130 when abroad?
If that is the case, then I would say it should be on a Q plate and go through iva.
But that is my view, based on some back street modifier and it no longer having the original chassis.