Originally Posted by Solstic

Correct.

The guard needs to be eliminated. Being in support is not enough and it's not required that you get the last hit. SEGs are included in the restriction lift.

I think you meant to type 'being in support is enough'. You are able to encounter a new EG/SEG whenever an EG/SEG that you have attacked at least once gets eliminated. That's why its' a good idea to poke lots of elite guards, super or not.