Athens has only TAA, TAB and some TAH. Rarely you might see TAE & TAZ, but there're taxis from another regions (for example someone driving from Corinth or Chalkis to Athens)
Thessaloniki has only TAE, those TAZ that you're seeing are from another regions (for example Chalkidiki, Kilkis or Serres)
EviaForever Athens has only TAA, TAB and some TAH. Rarely you might see TAE & TAZ, but there're taxis from another regions (for example someone driving from Corinth or Chalkis to Athens)
Thessaloniki has only TAE, those TAZ that you're seeing are from another regions (for example Chalkidiki, Kilkis or Serres)
For TAZ you mean they got the plates from there right? Because they are a blue-white classic taxi here.