You are absolutely right, it is strange and I had not noticed it before. I have gone back to my original source to check if I had made an error in transcribing the quote. My source was a hard copy of "Selections from the Dispatches and General Orders of Field Marshal The Duke of Wellington" 1851 Edition. The General Order of 9 May 1815 is given at the bottom of page 844 and, having checked, is exactly as I have quoted.

I have found exactly the same words quoted in my electronic copy of "General Orders of Field Marshal The Duke of Wellington" 1837 Edition and also my electronic copy of Wellington's Supplementary Dispatches Volume 10.

The 2nd paragraph of this General Order is a bit odd, speaking of "some of the light infantry battalions of each brigade", when there was only one such battalion per brigade. Perhaps it means some men in each battalion, but even then it is still strange.

Rod