Excellent post, The only things I would add are that, not only where eggs different in the 18th century but wheat was also different. Also, the thicker a dried noodle is the longer it takes to cook. 18th century pasta was nothing like Kraft Mac-N-Cheese noodles. In the winter I make homemade pasta 1-3 times a week. You haven't lived until you've had your favorite pasta made fresh.Ah yes you have hit upon another one of those problems with 18th century "English" sources for information..., what they called "boiling" was not what we sometimes refer to as a "rolling boil".... You find terms such as "boil it softly" and "boil it gentle". Boil in the case of old cooking instructions sometimes means when the water first shows signs of bubbles forming in the liquid, and other times often means what we call a simmer. Modern directions for Kraft Mac-n-Cheese show, "Boil water in medium saucepan. Stir in macaroni. Cook 7 to 8 min." Now if you put the macaroni in when bubbles first appear in the water, then bring it up to a "moving boil" you may be talking more like 12 minutes...add the fact the macaroni back then was more like very eggy egg noodles as Carbon 6 pointed out, and you get your additional 8 minutes for the full 20, and they didn't apparently like pasta "al dente".
Another problem I've had is trying to make stuff that called for eggs...., my first versions were very eggy flavored...until an excellent cook of 18th century cuisine told me to switch away from modern eggs....grade A large are too large for an 18th century dish. Grade A "medium" eggs are much closer, and yes the Colonial egg dishes made with medium eggs in the quantities specified, are much better (imho).