Greeting Mike, welcome to this forum.
To start, the so called "codes" refer to lines on the ship's plans, and have nothing to do with the planking. All these plan lines are there to enable the builder to make the correct hull shape and form, from plans drawn in two dimensions of a three dimension hull.
Planking is not easy, nor is the explanation of it. When I started, I went and photographed as many boats as I could, trying to get all the angles covered, bow, stern, shoulder, midships, etc. You are correct in that the finished article has planks that appear all the same width, and running parallel. but when closely examined you'll see tapering at ends and widening in the middle.
I can point you to a very good article that I have a copy of and which I could send you if you contact me via a "private message". The article appeared in a sister magazine in March 2009. The author was Robin Burnham and the article title is "Clinkered Boat Hulls", with a sub-title "traditional boat-building techniques adapted for the scratch builder."
The article takes the builder step by step through the art of clinker planking and explains many of the procedures to ensure a neat, satisfactory finish.
Planking is an art form, not easy, but with practice becomes easier. Paint and filler can hide many mistakes, but a good clinker planked hull is a work of art.
Kimosubby