Great news. I will set your account to developer. But beware, we have over 1200 icons now 
There’s a C file that defines and lists the available icons. And in Bforartist you can check the code of what icon is used. That way you can orient better in the icon sheet. I have separated the code to match the lines in the iconsheet.
The C file is UI_icons.c, and is located here: https://github.com/Bforartists/Bforartists/blob/master/source/blender/editors/include/UI_icons.h
For checking the code and to find out the name of the icon, switch to scripting layout, right click at a button, and choose Edit source. The text editor should open the code with this button and the used icon. And with this icon name you can find it in the sheet then. This method does just work with icons in the python code though …
I made the icons first with Gimp as bitmaps, and converted them to vector graphics when done. My collection of those bitmap files is a big mess though. Highly unorganized, i added folders when i had finished something. And i guess you want to redesign the one or another icon too. So i am not sure if it is of use for you.