The National Panasonics from the late 70's to the mid 80's all had woodgrain cabinets, at least in Australia.
Mum's is from 84 and it looks similiar, but older with Chrome highlights and a mishmash or Brown, Woodgrain and Chrome. Both Grandparents had models from 81 and they have lots of chrome, with a splash of brown and the woodgrain cabinets, they also have a raised door handle with a button on it to open the door.
That shape door button is late 80's early 90's at least with what we had in AU.
I dont know about the rest of the work, but all Panasonic stuff was Branded National or National Panasonic up until the mid 80's here, so by calling it Panasonic again its dated to the late 80's, early 90's, when the switch from brown to white occured.
Mum's is still in perfect condition and still going strong at 25 years old. Its main uses have been defrosting, reheating and cooking vegetables, so its never had a hard life.