I've also noticed this in the past. There indeed seem to be two different cases. The TAG Heuer logo at the bottom of the case is linked with the model no. CAL2110. The lack of the logo is usually seen on model no. CAL2110-0. It seems that both are genuine, with the CAL2110-0 being the rarer of the two. Unfortunately I haven't been able to find more about the reason for this, but I believe both are still Cal 12 linear systems and authentic.