The suffix is added by the supplier and can be any letter, which usually refers to a brand. Sometimes Genuine parts are labelled with a 'G' suffix, but not always.
The packaging of the OEM parts depends on both the supplier and the manufacturer. The same goes for the stamp - some manufacturers may well stamp on the part but this depends on the individual manufacturer.
It is likely the OEM parts will have a different finish than the genuine part, not being genuine version.
They are often made in the same factory, but the genuine original parts may have a different specification which may explain a slightly different finish and will also often have the Land Rover stamp on them.
its not quite as simple as it seems ,many parts we buy are no longer current ie made for lr as they are non current vehicles ,or factory/firm no longer exists as was, as said if you buy timken bearings they are the same as lr bought so are wabco products or adwest plus many more , a lucas horn would just be a lucas horn at the time but they dont exist as they did so a genuine horn now wouldnt be the same as lr originally bought as such