Soldiers never 'switched' they compensated though drill, drill and more drill. IF a soldier switched, he would interfer with the soldier to his rights firing. PLUS, if you switched, the hammer, with cap would be in your face, not somewhat protected by the rifle barrel, so the cap exploding would go directly into the face.
You are correct on the photos, depending on the method used by the photographer, some photos are reversed. Some 'modern' photographers, using period methods, even include props (jugs, boxes> on which the wording is reveresed, so that when the photo is take, it looks 'normal.'
JIM T