Complex sentence: The differences are not easy to spot as earlier models developed & changed but remained designated as Mk1, and the easiest way to differentiate between the various models is through the prefix at the beginning of the serial number which is located beneath the barrel joint.
Split into simpler sentences: The differences are not easy to spot as earlier models developed and changed but still remained designated as Mk1. The easiest way to differentiate between the various models is through the serial number prefix located beneath the barrel joint.