The piece above the moldboard was called a cover board. It made sure that the top layer of soil material being cut by the coulter and turned by the moldboard got completely under as the plow moved forward. The cover boards wear more quicly than the moldboard.
Some coulters were serrated for more effective cut of corn stalks, again allowing better cover.
The real wear part is the plow points, bolted to the bottom of the moldboard. Older plows had plowshares at the bottom which were generally heavier and more costly than the points. We always took shares to a shop for a new welded nose whereas the lighter/cheaper points were just replaced.
Several types of tripping mechanisms were used to protect the plow when it struck large rocks, etc. A hydraulic rig was used as well as spring loaded devices. Both allowed the whole bottom to kick back. These were a far cry from old pull type plows that were attached to the drawbar via a clevis. When you hit a rock, the whole plow stopped and jumped off the clevis, also breaking the trip rope (for mechanical raising/lowering) away from the tractor.