Stock 5" pockets on a GC3 have a miter angle of 142/143 variable because Brunswick couldn't hold the same miter angle on both sides of the corner pockets for what ever reason.
But, starting from the point of the corner pocket on each side, if the pockets are parallel to each other the miter angles would be 135 degrees, meaning cut at a 45 degree miter, making both sides equal at the mouth and throat of the pocket, which in turn deflects the balls being pocketed deeper into the throat, hence, pocketing balls more easily.
At 142 degrees miter on both pocket angles creates a funnel effect, meaning the throat opening gets tighter/smaller the further back a ball goes.
Each degree is equal to a 1/16" of a change in pocket opening per side, so the throat of the pocket at the pocket casting would measure no larger than 4 1/4". That means 2 balls placed in the pocket opening wouldn't touch each other in the mouth of the pocket, but wouldn't pass by each other either in the throat because the throat of the pocket isn't wide enough to allow that. That is what was changed on this table, the throat of the pocket was widened purposely to accept balls that might not go in otherwise, and that takes intent, and don't happen just because the rail cushions were replaced.