I used to work at a plant that made very similar dashboards for GM. The line you see is referred to as read-through, it is a result of a combination of processes. The first is a laser scoring process, where the cover (the part you can see) is scored from the back side, with a laser, about halfway through the thickness, in a specific dashed line-type pattern. This scoring creates a weak point in the dash so that when (if) the airbag deploys, it breaks through a controlled area, instead of randomly tearing the dash into jagged fragments and creating unpredictable shrapnel, which would be much more likely to harm the passenger in the path of the airbag. That line you see is the hinge portion of the door, which is designed to stay intact during deployment and keep the door from itself becoming shrapnel. The scoring itself however, does not make the line visible from the "A" surface, or the side you see. That is a result of the second part of the process, where a "PAB" (Passenger Air Bag) chute is vibration welded to the back side of the dash. This PAB chute is designed to hold the airbag module up against the back of the dash securely and in a very high tolerance location so that it will deploy through the door, created by the scoring process. It must be aligned just right so that the airbag does not contact the edge of the opening during deployment, because doing so may tear the bag and render it ineffective. The pressures and frequencies used during the vibration welding process cause the two different materials of the dash board and the chute to meld together and form a very strong bond, which can withstand the explosive force of the airbag deployment. Speaking from personal experience dealing with this particular type of read-through, it can be very difficult to maintain the integrity of the weld, and at the same time satisfy the appearance standards of automotive interiors. There are many factors in the manufacturing process that can change on a seasonal or even sometimes daily basis, that can cause the read-through to come and go. This would explain why you may see it more easily on some vehicles than others, and some not at all. OEMs such as Toyota or GM will always place occupant safety above appearance, so they are a little more lenient on appearance issues such as this one, but you can bet that the suppliers that make the dash boards are being driven to minimize the lines as much as possible. I fought this exact battle for almost 3 years at my last job, and now that I'm no longer in the automotive industry, my stress level has gone from a 9/10 down to about a 3.