On a roll here. Make of this what you will.

"The allied armies having now joined, Paris was soon in our possession; and on the 24th July the whole of the British army was formed in contiguous close columns on the great road from Paris to Neuilly. At 12 o'clock the allied sovereigns arrived, and rode down the front;

We then moved from the right, and in quarter distance columns marched down the Champ Elysees, where we had the honour of marching past them, they having taken up their posts in the Place Louis Quinze. When the 28th passed, the Duke was seen to point them out. The men were still in their ragged clothes; the colour-staffs were shot to pieces; one of them was two yards long, the other only one. I had afterwards the satisfaction of marching the regiment through the capital of France, and returned to the camp. We could only then muster four companies.

By the beginning of August the quartermaster, who had been sent to Deal for the new clothing, returned, when the "Slashers" very soon resumed their usual appearance."

('Narrative of the campaigns of the twenty-eighth regiment, since their return from Egypt in 1802.' Charles Cadell, 1835) p.240-41

Cadell gives repeated accounts of the regiment's caps being shot through during actions in Spain (along with many other regiments, not doubt) and there is this interesting detail from April 1814, following the cessation of hostilties:

"We received orders to prepare to embark for America. Fortunately for us, our clothing had been lost in the Bay of Biscay, on the way out, and being in rags, we were ordered home, destined to reap more honourable laurels." p.226

Yet it appears that the 28th took the field the following year wearing the old model of cap, three years after it was superseded.