The legal requirement is defined by rate of decel. For the original Volt (2011-2015), using L isn't aggressive enough to hit this requirement - so it isn't implemented. There is no difference in regen for 2014 and 2016 ELRs when using 'L', and all ELRs brake lights do come on when slowing sufficiently using 'L'. Also comes on with the paddles - which the old Volt didn't have.That isn't correct for 2014 ELR, 2011-2015 Volt.
The only difference with 2016 ELRs regarding braking is that they have a better blended brake feel when using the actual brake.