that number is like an internal number for device generations. iphones also have those. For example, iphone 15 pro max model is iPhone 16,2 and regular iphone 15 is iPhone15,4 or iphone se 3 model is iPhone 14,6 or iphone 6s+ is iPhone8,2 it is used for identifying the devices exactly, like iphone 15 and 15 pro and 15 pro max has diffrent identifiers. In your case a series 9 45mm and 41 mm has different identifiers.
safari on my phone, firefox on my pc