What does "invalidate" mean in "this did not include these invalidated home"?

I've never heard that use, but it may be another way of saying invalided out, which I take to mean, removed from the field of battle due to an injury. It may be only used in BrE and has a WWI feel to it.

A web search gives this from Longman's Dictionary

be invalided out (also be invalided home): British English

to have to leave the army, navy etc because you are ill or injured

“Invalidated” in this context is a rare synonym for “disabled,” used particularly of soldiers. Someone who is disabled by injury is an invalid (in American English, pronounced differently from the adjective that means “not valid,” with the stress on the first syllable and the vowel of the second syllable reduced). This sense of invalidated seems to be primarily from what is now the Commonwealth, in the early 20th century.

Google Ngrams shows that the phrase “invalidated soldiers” peaks at the height of the First World War, the handful of later instances are mostly from history books, and it is not common enough in the American English corpus to be indexed. I also cannot find any usages of civilians being “invalidated” by accident or illness. I have never heard invalidated used that way in modern English, but Google knows of at least one example of it being used in American English, in the Proceedings of the National Conference of Social Work in 1917.

Some examples (with emphasis added), from Canada:

Many ex-soldiers returned from Europe disabled and unfit to farm. Finding work could be very difficult for disabled veterans, though this issue was not ignored. A 1918 circular by the "Invalidated Soldiers Commission" was published in Ottawa with the aim of providing guidance on how to reintegrate these men into the work force.

St. Vincent and the Grenadines, also describing the Armistice in 1918:

On the day of the official celebrations ‘peace bonfires’ were lit at 8 p.m. at different points from Fancy to Union Island. On July 24, ‘invalidated’ soldiers were given five shillings and the ‘destitute poor’ two shillings [....]

And New Zealand in 1940:

A statement concerning the Government’s treatment of soldiers invalidated from overseas was made today by Hon. Mr Jones. Full provision has been made for the treatment and and rehabilitation of men when they return, including medical, boarding and classification treatment where necessary, pay and pension while in hospital, provision of [illegible] clothing allowance, traveling warrants, etc.

It means that the number of officers lost which is mentioned in this passage (282) did not include those who were sent home because they were made invalid by military conflicts.

Invalidate seems indeed to be a variant of the verb invalid here. Wikipedia has a note about a British officer, which says:

William Lawford (1809–1812), wounded and invalidated home during the Siege of Ciudad Rodrigo.

When you click on his name, you find a post which contains this sentence:

On his first experience of battle, a relatively minor engagement in the Pyrenees, Girdwood suffers a complete mental breakdown and is invalided home.

The AHD which you quote in your OP, has this definition of invalid as a verb:

Chiefly British: To release or exempt from duty because of ill health:

• I was not quite sick enough to be invalided out, even though I was of no more use (Mary Lee Settle).

The rest of the paragraph, specifically the next sentence, gives context and makes the meaning fairly clear.

The heavy drain, physical and mental, in keeping squadrons on the East African coast was reflected in the loss of 282 officers and men in the ten years 1875-85; and this did not include these invalidated home. Navy personnel, wracked by fever, sunstroke and dysentery, were forced to retire prematurely and live on a small pittance.

"Invalidated home" means sent home due to illness because they were incapable of duty