Lewis, Mauser salt blued the Luger starting late in 1937. So Lugers that you mentioned would have been salt blued by Mauser. The 1914 Erfurt Artillery I am doing for you will be rust blued and a little rougher in finish than a DWM ARtillery Luger.
Make sure on your later Mauser Lugers that they dont display rounded edges or over buffing that would indicate someone has reblued them. BYF Lugers from Mauser will also have a lot of tranverse polish marks especially across the top of the toggle links, breechblock and chamber, they will not appear mirror polish if original.