mootini - On my 18-inch Mooto X YBB frame, I am running a 100mm, -6... red. Because red = fast!
Jerome - I'm not sure that I understand your question.
With the Fox F29 forks...
- The 100mm version can be shortened to 80mm
- The 120mm version can be shortened to 100mm
On my Lynskey, I am running a 120mm that is reduced to 100mm and on my Moots Mooto X YBB I am running a 100mm that was previously shortened to 80mm for my 2011 Mooto X YBB (I opened the fork, pulled the 20mm spacer and changed the fluid). Both have the 15QR (I couldn't agree more with Jon's 15QR comment), but I feel that the 120mm version is a little stiffer probably due to the increased overlap of the upper and lower legs.
I think that the only way that you will know for sure if Fox set the fork to 100mm is to search for the measurement from the crown race to the fork dropouts... then measure your fork. I can't see why they wouldn't have done what they said that they would do.