The fault presents as a band of underexposure across part of the frame, caused by the shutter not functioning normally. It is most visible at faster shutter speeds and against even tones such as sky or a plain wall.
Nikon's affected manufacturing window widened after the original announcement: from October 2014 through June 2015, extended in July 2017 to also cover July 2014 through September 2014 and July 2015 through September 2016.
The practical consequence for a used buyer is that serial number verification matters more than shutter count, and that a body whose advisory work was never carried out remains affected today.