This s/n 331859 is part of a s/n 331601 - 332100 "run" of 200 Hunter cased and 300 Open faced Currier Transitional movement's Illinois did in 1883.

It is clear to me they made 500 Hunter movements and then added a 5th pinion to some and made Open Face watches too. These attached pics show my HC currier, and the discussion item with added 5th pinion to make it open faced.

The added "twist" is these are all 13 Jewel movements with 3 sets of paired jewels in the main train. So we have a SW/KW Transition, Model 3, 13 Jewel Currier OPEN FACE 5TH PINION. Shugart shows some things near this description, but nothing "hits the nail on the head". Is this Rare?