Rust blued interiors?

Although I have not personally observed this, it is noted by Jan Sill that the later 1936 thru the rust blue 1937 period Lugers did not have polished interiors. If this is the case, how did this difference manifest itself? The implication is and I've always believed that the pre mid-1936 Lugers were polished on the inside AFTER being rust blued. Therefore these Lugers were bright on the inside. The post mid-1936 Lugers (rust-blued) were not polished on the inside and therefore not at least completley bright.