The certificate allows them to bypass waiting periods on pre-ex if they transfer from one group plan to another without a break in coverage. In most states it means nothing if you are going from group to individual.
Just to add to that (in some states at least), if you go from Group to Individual and the carrier accepts the condition without putting an exclusionary rider on it, then the Individual plan must credit the time served on the prior coverage against the waiting period on pre-existing conditions. In my primary states, this also goes for individual to indiviudal.
For indie plans like Aetna it means all the difference in the world. With prior credible coverage the 12 mo. pre-ex period Aetna imposes for any condition treated in the last six months is waived. Other carriers give partial credit towards pre-ex waiting periods.
HIPAA rules for individual to individual, or group to individual, do not apply in GA. Some carriers (as you mentioned) give credit for prior coverage. To my knowledge only Aetna & Consumer Life do so in GA.
Unless you are applying as a HIPAA eligible, the regular underwriting rules apply and riders, rate ups or declines will apply.