Fuse numbering, is this correct?
 

It looks like from an actual hardware perspective the Fuse box is in 2 blocks, a 10 fuse block and an 8 fuse block and numbered as such (left to Right looking at the exposed fuses) I considered this to be 18 (1-18 left to right) fuses however, if I understand the Current flow diagram it would appear the reverse i.e. its starts at S2 I presume as S1 (Far right) is not used (Mine is unused), the current flow diagram fuses are identified S18-S2 left to right, S21 I cant identify although its in the current flow index/key with no location, S22,S23 & S24 are identified as being on the Regulator Panel. No mention of an S19 & S20 ! Is this correct ? may explain why I'm struggling.

Cheers
Mark

I am no more clear on the wiring than you, but these two threads may help confirm some of what you have figured out and help further.

Look at post #13
http://forums.pelicanparts.com/porsche-911-technical-forum/940491-ac-problems-keep-blowing-fuse-19-a.html

http://forums.pelicanparts.com/porsche-911-technical-forum/170417-fuse-panel-diagram-picture.html