In Europe the Lightning rules of the Railways are different to US American RailRoads.
In the early Steam Era, each Railway Company used their own rules.
In later years the companies became mostly state Railways than the State created some specific guidelines to each State Railway.
Great Britain is different to the Continental European Nations, sure it was the Motherland of the Railways but each Nation used their own railway Laws and Rules.
In Germany as example, the Imperial Kingdom gave own Instructions for Double Track Mainlines and Branchlines.
On the Front of any Loco or railcar it was enough to have in Minimum 1 Lantern mounted above the smokebox or below the smokestack better are two.
The headlight Position in addition two the other one or two lower Lanterns was only valid Single Track Lines.
This rule had been replaced in 1937 by Establishment of the DR - Deutsche Reichsbahn.
Before 1910 it gave differences in the shown lights, by Special Causes. All Front lanterns were Used for signalling, too.
If a Train moved by double track onto wrong side, than in the front needed to be displayed a red light on the lower position onto the Center beam.
If a Second Train moved into Short Distance to the First Train in Same Signal Block, than the Headlight of the First Train needed to Show a Green light, the Last Train needed to show a white light.
The end of Train devices had Special rules in addition.
In the Year of 1937 the DR made bigger changes to all Existing rules of the Railways in germany.