I can confirm this--the later platinum Pluses came in the white boxes with the red Apple on the side and the gray drawing of the computer on the front. I have a platinum Plus made in the 49th week of 1989 with such a box.

There are manual variants out there as well to match these boxes and also to go along with system updates. The 1989 Plus manual wouldn't talk about the single, unified control panel from the pre-System 6 days, for example.