18.104.22.1689 is the latest Extended Support Release which only contains security fixes and does not contain any new features or non-security bug fixes implemented since 11-Aug-2015. 22.214.171.1246 is the latest stable release which contains security updates as well as new features and other bug fixes.
You can review the Flash Player Release Notes to compare the features and non-security bug fixes implemented since 11-Aug-2015.
If you which to remain on 126.96.36.1999 you do not need to update to 188.8.131.526. If you which to take advantage of new features and all bug fixes (security and non-security) implemented since 11-Aug-2015 then you should update to 184.108.40.2066.