just received a small 31; was following this string for a while....upon receiving mine of course I pushed on the spine to judge for myself.. it had a slight "looseness" in comparison to my Small Inkosi which is butter smooth and "rock" solid. None the less I took the 31 apart as I am designing a backspace and will machine myself. Since it was all apart I cleaned it and re-lubed it just because I had it apart. After assembly I checked the rock again... there was absolutely NONE. I really think the issue is a non-issue and for those that it bothers, I wonder if they took the time to disassemble/clean/lube/reassemble it would change anything.
BTW... as a new owner of a Chris Reeve knife (knives) I am extremely happy with both of them and honestly, the Small Inkosi for me is one that had I have to chose one knife (I have a reasonable collection Benchmade, Curtis, southergrind, Spyderco....) I would without hesitation carry the Inkosi with no regret.