How far does the breastplate extend down? Can you bend at the stomach? Wil the placard slide over the breastplate?

Many breastplates were meant only to cover down to the bottom of the ribs. They're called breastplates, not torsoplates after all. :) Many poor reproductions try to cover down to the navel or waist, which would make bending very difficult.

Michael,

As a general 'rule of thumb', the waist of the breastplate should be about where the elbow comes. Many modern armourers tend to make the waist far too low, which makes it more of a corset than a breastplate! Armour should never be so inflexible that you can't move in it freely, genuine armour is extremely flexible !

Regards ,

Russ

Though the plackard is never articulated, the breastplate ends at the lowest at the navel, with the fauld covering the rest of the torso. So that's how it flexes.
-Wilhelm