Parker 45 Flighters nib grades

This photo is an attempt to show the nib grades on my three 1970s Parker 45 'Flighters'.

The pen with the 14k 'M' nib was 'MADE IN ENGLAND' in the early 1970s;
the pen with the steel 'X' nib was 'MADE IN FRANCE' in the early 1970s;
the pen with the steel 'M' nib was 'MADE IN ENGLAND' in the mid-late 1970s.