All of the big companies bring out new models in their production runs the minor problem in what they produce in the quantity. For example 2000 of 30 different model types.
Until the items are released its difficult to gauge which ones will sell well. All the 30 different models produced, some would sell faster than others, that is not to say a slow moving model is no good, (some of the slower sellers are the best) so in fact a slow selling model could take a couple of years to sell so that the date of release could be the key to how old the model is. (Car manufactures can store cars up to 5 years; you buy what you think is a brand new car. With new registration 3 years no MOT it could be 8 years before the car has its first MOT) Anther factor on die-cast models is how the item is stored and long its been on the shop shelve or warehouse this can effect the quality of the Item. Good selling items can be produced again and again so although the item was released say in 2002 it may have been produced in 2006. Anther bugbear about, is that some manufactures do not Record dates of manufacture of the Die-cast models only by making painful research on each item can you find out the D.O.M. When you order models from the Manufactures and look at the pictures given to you look at the die-cast Companies web site and find that the actual model you are selling has variations, some examples wheel hubs, wheel trims, and at worst different colours.