Just like how with the new system for stockpiles you start out not knowing whats going on (we have around 200 seeds, and about 5000 limestone) and as your broker gets better and spends more time assaying your stocks you get better indications of what you have it would be fun if such a system was extended to the monsters.
Adventurer standpoint - You recieve a quest to slay Durg, a troll living in a nearby cave. You know nothing about trolls, and less about Durg in particular. You go forth and slay Durg after a mighty conflict. You now now more about trolls. As you kill and encounter more of their ilk you will get better at identifying them.
Conversely you could consult a sage, who in exchange for coin might tell you that "Durg is a massive example of his species, as strong as 10 men, and with a stride that covers 10 feet!"
Fortress standpoint - The addition of a librarian/sage noble to your roster. He would gather the corpses of dead creatures, and study live ones in cages. Over time he would gain knowledge of the creatures and your identification skills would rise. Looking at a Dragon at the start of the game would give the message..
Ur Draco
Red Dragon
Massive
Ur Draco is a dragon. It is massive compared to you. It is red. It has wings.
So only information that can be gained from looking at it. Looking at the same dragon when your fortress has a librarian with some knowledge of dragons...
Ur Draco
Red Dragon
Male
Healthy
Massive
Flier
Ur Draco is a Dragon. He is over 40 feet at the shoulder, above average for his species. He looks healthy, and well fed. He is a mature example of his species, the Red Dragon.
Red Dragons are cumbersome fliers. An adult Red Dragon is a dangerous foe for even a group of dwarves.
Ur Draco is known to be a particularly vicious example of his species.
So more detailed information, with some specifics about the dragon and some about the species. With a detailed knowledge of dragons...
Ur Draco
Red Dragon
Male
Healthy
Massive
Flier
Ur Draco is a Dragon. He is over 40 feet high at the shoulder, above average for his species. He is 200 feet long, above average for his species. He probobly weighs around 200 tonnes. He is a mature example of his species, the Red Dragon.
Red Dragons are cumbersome fliers. Red Dragons are highly territorial. Red Dragons can breath fire at will, and their flames can consume even the less noble stones of the mountain. Red Dragons will gladly consume humanoids, and revel in doing so. Red Dragons are rarely slain, they are stronger than a dozen normal dwarves and they can attack with their tails, teeth, claws and fire. Red Dragons are highly intelligent. Red Dragons will flee when threatened with vast armies. Red Dragons hate the smell of Lupine Violet Oil, and will avoid areas where it is present in any great quantity.
Ur Draco destroyed the City of Nonenheim in 2045. Ur Draco slew Nildran, the elf prince, in 2046. Ur Draco is angry.
So as you learn more about Dragons you get more and more specific and useful info on an inspection.
The entry for Ur Draco would inherit description items from Dragons, Red Dragons, and his specific history. This would be separate from the actual "stats" entry and be arranged so that the better the sage you had, the more useful information you would get.