Yeah, the whole "Innovations" part is the real complicated thing. I don't know nothing about programming, so it's hard for me, to implement a "rule" set for that kind of thing. But crudely I imagine it in the following way.
The World generating starts with default weapon/armour. Every Civilization has a chance to make an innovation in one category (swords,crossbows,gauntlets) based on time and events, like inbetween wars, after lost battles, after mega Beast attacks. Innovations should only occur if the involved Civilization part(Castle, Fortress, Town) has survived the trigger event. Innovations should only be possible by highly skilled individuals and must be rare. Innovations made by your Fortress should quickly adopt by your Civilization and vice versa. Each innovation stacks chronologically on items. Innovations should be object specific, this means a property for long swords, are not valid for short or two-handed swords and vice versa. Every innovation can only occur once each category (no double thickness Armour). Each item category has it's own pool of possible innovations.
You asked yourself why the "Inventor" and "Date" Description? First, I think it's pretty Dwarf Fortress like. Second, if you have Fashion invented dates, than you can assume one object's age. Not in a explicit manner, but more in a "epoch" categorized manner.
Possible Gameplay Feature 2: "Antiques"
Example 4:
xThe Tomes of Flickering copper spear x
This is a copper spear, in a "The Tomes of Flickering" Fashion. It has a leaf-shaped head. This was invented by the Dwarf Weaponsmith "Kadol Tulonzatan" in the Year 64. It has two prominent wings at the base of the Head. This was invented by the Dwarf Weaponsmith "Kadol Tulonzatan" in the Year 112. This object shows some wear.
We presuppose that you find this object in a abundant Fortress in the actual Year 550. "The Tomes of Flickering" is an extinct Civilization. They where wiped out by a Hydra, in the Year 150. So you can assume, this spear is at least 400 years old and becomes an antique object, for every intelligent creature, with the sufficient historical information.
This also works for your home Civilization.
Example 5:
+The Passionate Bodices steel mail shirt+
This is a finely-crafted steel mail shirt, in a "The Passionate Bodices" Fashion. It has a 2 to 4 grid pattern. This was invented by the Dwarf Armourer "Kadôl Dorenthortith" in the Year 121. The single ring-pieces are wedge-shaped. This was invented by the Dwarf Armourer "Melbil Nishevost" in the Year 165. The composing rings are tightly riveted. This was invented by the Dwarf Armourer "Imush Udibkib" in the Year 224. The mail itself is made in alternating rows. This was invented by the Dwarf Armourer "Imush Udibkib" in the Year 258.
Again we presuppose that the "The Passionate Bodices" are your home Civilization and the "Example 5" mail shirt with 4 properties, is the actual Fashion in the Year 300. So every other mail shirt, in a "The Passionate Bodices" Fashion you find, by goblin loot, tombs, tower zombies, old battlefields, with less than 4 properties, is automatically from an older "epoch".
The deal is, that every weapon/armour has not only their value based on material and quality, but also by age. Than you can make extra Museums, with antique Armoury, from long ago fallen Civilizations or Ancestors, and every Dwarf that see that, get the thought how briefly our time is in this Universe... begone fear!
Do you understand what I mean?