pxCoverInsKey is the pzInsKey of the Parent case. The name "Cover" says it is the key of Parent. pxCoverInsKey is available in every child case in order to identify its parent. For every child case, the parent is identified using pxCoverInsKey.
pxCoveredInsKey: pxCoveredInsKey is the pzInsKey of Child Case. For every Parent case can have multiple child cases, all these pzInkseys of child cases are holded in parent in "pxCoveredInsKey".
pxCoveredInskey can be a List Property as it holds more than One Child Case Identification Key.