Well...........what about Peter's badge?
I think that somebody stuck a longer than normal slider on it so that it could be worn on an item of headgear that warranted a longer than normal fixing to ensure it didn't fall out whilst charging headlong, yelling loudly with fixed bayonet into a skirmish...............perhaps behind a piece of cloth worn around a Foreign Service Helmet or something similar.
Or perhaps so that it could be pushed further down into a FSC and the wearer would be able to scratch any itch on the front of his head, without having to remove his cap.....important on parade perhaps.
Or just adapted so that it could be removed from the headwear being worn at the time and used as a tea stirrer.
Or, howabout a wily soldier putting it on his badge for the occasions when (there was no straw available because it had been used for horse feed) whoever drew the short straw had to undertake an onerous task, and badge sliders were substituted for straw.
Or some sliders were wrongly manufactured longer than required, but still fixed to badges and issued to troops.
Or the answer could be as simple as we'll never really know until dress regulations explaining the use of a long slider are discovered.
Regards
Brian