Well, of course, the best way to find out for is to ask them what they shipped. I can't speak specifically for them but generally, all sources ship bulbs about 16 to 18 cm size. There are several reasons for this, amongst them and perhaps the most important to the customer, is that 16 to 18cm is the optimum size for ease of garden planting and adaptability into the customers garden. Other reasons are that it coincides with the growers 3 year crop rotation, takes up less bin processing space, refrigerator space and expense, and, saves the customer money in shipping by getting more bulbs per box, just to name a few.
Keep in mind some hybrid cultivars grow bigger bulbs than others so some bulbs may be shipped over the 16 to 18 cm size. If they are less than that it is usually stated. Exactly what size is characteristic for Gold Band and how that relates to the overall lilium population in terms of size relative to shipping size, I'd rather have someone else on this forum speak to that.