NTG1 = Up to Model Year 2008, W211 E, W219 CLS, R230 SL (MY05->), R171 SLK, W220 S (MY04->), W215 CL (MY04->)
NTG2 = W169 A, W245 B, W203 C (MY05->), W209 CLK (MY05->), W164 ML/GL. W251 R Class cars
NTG3 = W221 S, W216 CL (before MY2010)
NTG3.5 = W221 S, W216 CL, MY2010 onward
NTG4 = W204 C, W212 E, W207 E Coupe
NTG2.5 = Model Year 2009 and onward A, B, CLK, W211 E, CLS, ML, GL, R Class and Model Year 2008 until 2012 SLK
NB. CLC changed from NTG2 to NTG2.5 part way into Model Year 2009. W209 CLK never got NTG2.5.