Hello Stephen
Apologies, I may be jumping in here before you've posted your follow-up with 1914 details.
You're right to say that the 70th Foot were not involved in the march from Kabul to Kandahar in 1880, but neither were they present at the subsequent final battle. They were at Kandahar in the first stage of the campaign, reaching the city in Jan 1879, but by April 1879 the regiment were back in India, their part in the Afghan campaign over for good.
I don't know what your source is for Henry King being on the Kabul-Kandahar march, but perhaps it has come out of the fact that he did march to Kandahar, but from Quetta under General Biddulph at the start of the campaign, not the later march under Roberts for which a bronze star was awarded.
Best - Garen.