The SMLE handguards are relatively thin pieces of wood that fit atop the barrel and protect the rifleman's hands from the hot barrel.  Two 'fingers' or prongs extend from each handguard to wrap around the base of the backsight bed.  The handguards are actually a rather sophisticated piece of woodwork, requiring milling a curved piece of wood with dips and flutes. Many rear handguards are reinforced with strips of wood glued into kerfs sawn crosswise to the grain.

It is not hard to break one of the prongs off when removing the rear handguard.  And it is not unusual to encounter a SMLE that has had all of the top 'fingers' removed.  I once met a collector who was quite adamant that the ONLY 'reason' that the fingers were removed was so that specialist alpine troops could manipulate the backsight without taking off gloves or mittens.

This probably explains why the 1920's KING'S AFRICAN RIFLES recruit in the picture below is smiling.  His rifle is a SMLE MK III (with magazine cutoff) Type 1 (with volley sights) - and the 'fingers' around the backsight have been removed - a sure sign that this recruit has been selected for alpine training. (Did we get that right?)

British East Africa, birthplace of the KAR, is the home of Mt. Kilimanjaro (19,430 feet) in modern day Kenya. Malcom Page's A History of The King's African Rifles and East African Forces REF covers the history of the KAR from start to finish.  And while climbing 'Mt. Kili' is mentioned once or twice, there is no suggestion of any specialized troop training taking place on the slopes of Africa's highest peak.

Occam's Razor: (i.e., The simplest explanation is usually the correct explanation.) I think that when in the course of service one or more of the prongs got broken the simplest expedient was merely to trim the remaining prongs back to match.  Replacing the top handguards was deferred until if and when the rifle was returned to the depot level for other service.