A few years ago I did a heavy amount of researching and preparing for a lecture I gave at Costume College.
I had been asked to post this to my blog, so I am finally getting around to doing it!
Sleeves often overlapped, as most were two-piece sleeves.
The same was true of dresses of the 19th century- certain pieces overlapped, and by grouping together, you saw which seams matched as well as what pieces went together.
You may feel like you need a decipher to understand the markings.