Yes, these engraving slugs would fit in with the items being OSP. These slugs, either mounted on the surface or set in to item to provide a flush surface, are sometimes solid silver, sometimes very heavily plated and are there to take engravings, as the normal OSP silver surface would be penetrated by the graver exposing the copper under layer.
The crest is unusual (to me), it would be worthwhile I'm sure starting a new topic in the 'Family Crests' section with the clearest images that you can capture. Try putting one of the pieces into a freezer for 20 minutes, remove it, and then take the images, this will give the surface a fine mist covering and stop the reflection. Take the images in daylight with no flash and the camera set to the macro feature.