You can easily fix the graphical bug of the armour upgrades by changing their sequence in the EDU:

Code:
armour_ug_models Venetian_Archers, Venetian_Archers_ug1
should read:
armour_ug_models Venetian_Archers_ug1, Venetian_Archers
The same goes for Retinue Longbows or any other unit with this kind of bug.