Are you sure that is correct? The way that it was rolled out is that all stores were changing to the close to open shift diff for shifts before 4am. If you work a 4am shift, even though you have a 6am process, you should get the shift dif. The only difference should be between overnight stores closing at 10 and those closing at 11. At least that is how I understand it.
The idea was that you would not be depending on those shifts for extra pay and could instead take a mid or closing shift without a huge impact on your paycheck. The idea was to minimize the impact that it had on team members but to compensate those already with the company so they would not be impacted by the change.
100% positive. They rolled the shift diff into the base pay rate for those who used to get it but would have lost it by moving to the 6am process (those hired after were just SOL). I've worked many many shifts overnight / 4am in the years since then due to large planogram / signing workloads, but no shift differential for any of the team members.