Class Societies and many Countries Transportation Authorities over the years as a method of standardization have adopted a standard of numbering of surveyable machinery components from the forward end of a vessel. Class Societies consider each cylinder of a Main Engine regardless of the configuration with all it's components as independent surveyable items thus allowing a staggered overhaul cycle and eliminating the requirement to completely overhaul an engine every 5 years.
This can cause problems with European built medium speed engines when one identifies a unit by the manufacturer's designation rather than the Class Society standard and the surveyable equipment list. Engine manufacturers such as Pielsitck, Wartisila and MAK always number the cylinders from the flywheel end. Whereas most North American built engines ie Caterpillar, Detroit & EMD cylinders are numbered from the free end.
The Class Societies usually class a the complete auxiliary engine as a single surveyable item so cylinder numbering is not an issue. The location of the auxiliary engine in relation to the bow and the Port or Stbd side become the determining factors
Troubleshooting 101 "Don't over think it - K.I.S.S. it"