This is a boring slog, since all of these documents are much the same. However, they prove how Afghanistan looked at itself as a nation (state).

They also prove that Afghanistan was a state from 1923 to the present - the relevant period in Afghan constitutional history which encompasses the 1949 GCs, to which Afghanistan was and is a "High Contracting Party".

Geneva Conventions of 12 August 1949.
State Parties Afghanistan
Signature 08.12.1949
Ratification / Accession 26.09.1956
Reservation / Declaration - None
http://www.cicr.org/ihl.nsf/WebSign?...rm&id=375&ps=P

Constitution of Afghanistan (1923)

The Constitution of Afghanistan April 9, 1923
....
Article 1
Afghanistan Is Completely Free and Independent in the Administration of its Domestic and Foreign Affairs. All Parts and Areas of the Country Are under the Authority of His Majesty the King and Are to Be Treated as a Single Unit Without Discrimination Between Different Parts of the Country.
http://www.afghan-web.com/history/const/const1923.html

Constitution of Afghanistan (1964)

The Constitution of Afghanistan 1964
.....
Title One
The State
Article 1
Afghanistan Is a Constitutional Monarchy; an Independent, Unitary and Indivisible State. Sovereignty in Afghanistan Belongs to the Nation. The Afghan Nation Is Composed of All Those Individuals Who Possess the Citizenship of the State of Afghanistan in Accordance with the Provisions of the Law. The Word Afghan Shall Apply to Each Such Individual.
http://www.afghan-web.com/history/const/const1964.html

Constitution of Afghanistan (1976)

The Constitution of Afghanistan 1976
....
Chapter Three
The State
Article Twenty: Afghanistan Is a Republican, Democratic, Independent, Unitary and Indivisible State.
Article Twenty One: National Sovereignty in Afghanistan Belongs to the People. The Nation of Afghanistan Consists of All Those Individuals Who Hold the Citizenship of the State of Afghanistan in Accordance with the Provisions of the Law. The Word Afghan Shall Apply to Each and Every Individual of the Nation of Afghanistan.
http://www.afghan-web.com/history/const/const1976.html

Constitution of Afghanistan (1987)

The Constitution of Afghanistan 1987
....
Chapter One
Foundations of the Political System
Article One:
The Republic of Afghanistan Is an Independent Unitary and Indivisible State Having Sovereignty over the Whole of its Territory. The National Sovereignty in the Republic of Afghanistan Rests with the People. The People Exercise National Sovereignty Through Loya Jirga, National Assembly and Local Councils.
http://www.afghan-web.com/history/const/const1987.html

Constitution of Afghanistan (1990)

The Constitution of Afghanistan 1990
.....
Chapter One
Foundations of the Political System
Article One:
The Republic of Afghanistan Is an Independent, Unitary and Indivisible and Islamic State, Having Sovereignty over the Whole of its Territory. National Sovereignty in the Republic of Afghanistan Belongs to the People. The People Exercise National Sovereignty Through Loya Jirga and National Assembly.
http://www.afghan-web.com/history/const/const1990.html

Constitution of Afghanistan (2004)

The Constitution of the Islamic Republic of Afghanistan
(Ratified) January 26, 2004
....
Chapter One: State
Article One
Afghanistan shall be an Islamic Republic, independent, unitary and indivisible state.
Article Two
The sacred religion of Islam is the religion of the Islamic Republic of Afghanistan. Followers of other faiths shall be free within the bounds of law in the exercise and performance of their religious rituals.
Article Three
No law shall contravene the tenets and provisions of the holy religion of Islam in Afghanistan.
Article Four
National sovereignty in Afghanistan shall belong to the nation, manifested directly and through its elected representatives. The nation of Afghanistan is composed of all individuals who possess the citizenship of Afghanistan. The nation of Afghanistan shall be comprised of Pashtun, Tajik, Hazara, Uzbek, Turkman, Baluch, Pachaie, Nuristani, Aymaq, Arab, Qirghiz, Qizilbash, Gujur, Brahwui and other tribes. The word Afghan shall apply to every citizen of Afghanistan. No individual of the nation of Afghanistan shall be deprived of citizenship. The citizenship and asylum related matters shall be regulated by law.
OK, all of that proves that Afghanistan has been a nation (state) at all times relevant to this discussion. The next issue is the successive governments of Afghanistan - in short, who had authority to speak for the "High Contracting Party" under the 1949 GCs.