GFB offers 3 items for the Subaru Short Shifter:
• Short Shift GFB SUBARU STI 6speed Basic Kit NUMBER 4003
• Short Shift GFB SUBARU STI 6speed UPGRADE kit NUMBER 4202
• Short Shift GFB SUBARU STI 6speed SuperShort kit NUMBER 4002
The simplest way to describe the differences is this way:
4003 (basic kit) + 4202 (upgrade kit) = 4002 (SuperShort KIT). When the 4003 and the 4202 are added together, you get exactly the same parts as you do with the 4002.