Of course our question is does the narration in the contemporary sources gives away anything about the slaughter happened during the chasing phase of the battles.
I don't know much about annals but I do know that despite their seemingly matter-of-fact tone they are very biased. They were written from a specific point of view, influenced by (for example) the expectations of those who ordered their creation, cultural and religious prejudices, and written by people who were committed to their side and many times didn't have the experience about the events they wrote (monks living in monasteries). They got their information from already biased second-hand sources they heard about somebody who met someone who had a relative who seen somebody who had an acquaintance actually participating in the event.
The tales of the battles ... Fighting people are usually boastful and proud as fuck meanwhile insecure about their bravery. You know about the Law of the Ever Growing Numbers, Bernd? It's about the size of the two armies. "We are the good guys, badass as fuck. Of course our numbers are great." - so they overestimate of the amount of their own troops. It also helps with confidence issues, strength in numbers. But, they overestimate the number of the enemy as well. They have two reasons. If they win of course the enemy were numerous: "we are tough as fuck we can defeat large quantities of enemies". But if they lose: "we only lost because they were so many, it wasn't fair fight".
Grossman in his book mentions the tendency of soldiers of all ranks to beautify the truth when they give a report of their doings. Ofc this is generally true to everyone.
No, the soldiers are not apt to write of their failures or the failures of their men; with few exceptions, it is only the heroes and the glory that make their way into print.
In A History of Militarism, Alfred Vagts accuses military history, as an institution, of having played a large part in the process of militarizing minds. Vagts complains that military history is consistently written "with polemic purpose for the justification of individuals or armies and with small regard for socially relevant facts." He states, "A very large part of military history is written, if not for the express purpose of supporting an army's authority, at least with the intention of not hurting it, not revealing its secrets, avoiding the betrayal of weakness, vacillation, or distemper."
Vagts paints an image of military and historical institutions that for thousands of years have reinforced and supported each other in a process of mutual glorification and aggrandizement. To a certain extent, this is probably because those who are good at killing in war are quite often those who throughout history have hacked their way to power. The military and the politicians have been the same people for all but the most recent part of human history, and we know that the victor writes the history books.
It's a conspiracy, dude.