Not all gunstocks have lock panels that are the same on both sides. But American Longrifles do, in general.
The English devised a system that greatly increased the strength of that fragile section of wood at the breech where the barrel, lock, triggers side plate or washer necessarily remove a lot of wood, leaving the area prone to fracture. You see a lot of muzzleloading guns broken through the panel from the breech down through the rear lock screw...there just isn't much wood there.
Here's a device that helps with that problem. The patent breech is filed away on the off side just back of the end of the barrel, by as much as 1/8". the side panel can be the same thickness as the lock's panel, but with this extra 1/8" of wood in this critical spot, much strength and security is added to the stock. Here's a picture of a pistol with this feature...