According to Gong Chu's Memoir, both CPC and KMT army officers wrote detailed reports after every and each battle. This kind of activity is called After-Action Review (AAR) in today's military jargon. Since both KMT and CPC officers were trained in the same school, the question that follows is this: which military, German, French, Russian or English, started this tradition and explicitly put AAR in their army doctrine?
Napoleon's Marshals and Generals de Division all wrote up such - see for example Saski: Campagne de 1809 en Allegmagne et en Autriche.
An excerpt from Vol II:
which I have (very roughly) translated as:
GENERAL DE WRÈDE TO THE MAJOR GENERAL
Biburg, 15 April 1809
I have received this morning, at 9 o’clock, midway on the route between Eckmuhl and here, the order of Your Highness, dated yesterday at 4 in the afternoon. My retrograde movement is complete, and I believe not only can I maintain myself today in this position, but tomorrow as well, if Your Highness does not send me other orders.
The suburb of Landshut is now again occupied by my extreme advance posts; at least, I have not any new report that they have been forced to retire. But tonight I will be forced to withdraw them, [as] the Marshal the Duke of Danzig seeing my intent withdraws them by Geisenfeld to Rain. I will therefore withdraw the picket this evening to Pfaffenhausen and the one which I have on the route between Kelheim and Landshut, to Rottenburg, from where I will observe to my left and right the movements of the enemy.
Tomorrow, at break of day, all my infantry will establish a bivouac on the heights behind my position here.
Also if it ensues that the enemy does not march on Geisenfeld by my right, I can hold against 15,000 men if they attack me by my front or my left. I will maintain a precise co-ordination with M. the Marshal Duke of Auerstadt to inform him of everything which passes by this location.
I have a battalion at Vohburg which, at the moment that the enemy marches by Geisenfeld, has orders to carry itself into the bridgehead at Ingolstadt so as to ensure my retreat.
Awaiting other orders of Your Highness, I am … .
And this is just to ensure that (and which, as Berthier was causing the marshals to perform much retrograde marching until Napoleon's arrival in Bavaria) orders were received and correctly implemented.
It is very possible that the first full concept of an after action report originates at this time, as Napoleon originated the "Chief of Staff" concept with Berthier. (Note that at this time the designation "Major General" is a position, specifically that of Chief of Staff, and not a rank. Berthier was a General de Division (rank) and Marshal of France (properly a title, though often treated by its holders as a rank) like any other senior French Commander of the time.
The Prussian General Staff formation and army reorganization that was occurring at this same time would formalize the structure beyond Napoleon's "proof of concept".