Remember Me? Brassing, light all over discolouration. Parker XL. Some of these pens will incorporate early production materials, such as the caps and speedline filler. Also in The Parker "51" Signet was introduced with an all GF cap and barrel with vertical lines.
The RU designation continued on nibs through
Date coding a Parker 51
A smaller Demi pen was available from the beginning of the aerometric production. So my '8' would be either or Sep 29, Jul 13, and filler cap. Rules - Market Watch Rules. That's a really great source for information about production changes and dates.