I don't work for GM but I am an engineer in the auto industry so I can help decode it somewhat based on working for another company.
LH for driver side.
14057322 is probably the part number for the door panel if you ignore the color.
Change 9 probably means it is the 9th revision to the drawing for the part.
P2-3018 ?
All the 14057.... are the color specific part numbers for this door panel.
The grid is month of the year on top, year down the side. Each dot would be the month of production. This is a way to narrow down when the part was molded. By this grid, none were ever made in 1982. Starting in July of 1983 they put a dot in the mold and then made parts that first week. Starting the next week another dot would be put into the mold so that parts made starting that week would have two dots in that month, etc.
So when the mold was made at the tool shop they would put all the nice, neat letters and numbers. Once at the supplier that actually molds the parts all they have to do is use a punch and hammer to indicate month of production.
This is a somewhat crude way of tracking when the parts were made but works well if you start seeing bad parts at the assembly plant. You can at least track down what week the parts were made, compare that to tool maintenance, etc.
It is also interesting to note that for some months either they forgot to add the punch marks or didn't make any parts at all.
