I agree that some of the older numbers are worth quite a bit, however that really applies to those that have two letters and four numbers, or three letters and three numbers. The ones such as that attached to this car would really have no particular value at all, unless it could be read as a word. The number COM 1 C was particularly famous.
Even if a number were transferred prior to the car leaving the UK, the physical plates themselves would probably stay attached to the car. The plates themselves don't change hands, new ones showing the transferred number would have to be obtained.