Many Nikon DSLR's have an overlay function which combines (overlays) two NEF images to produce a third NEF image in-camera. The source images don't have to be different, so an image can be combined with itself, which is what I did for this example.
I have noticed that for such combined images, the WB for As Shot has Temp: 2880 and Tint: -119, regardless of the WB camera setting of the original images. In this example, I shot an image with my D750's WB set to Daylight. Importing the original image into Lr Classic 8.0 gives the As Shot WB as Temp: 5300 Tint: +7, which is always the value for this WB setting. See the screen-shot below:
If I change the WB from As Shot to Daylight, the values change slightly to Temp: 5500 Tint: +10, as shown:
Combining this image with itself using 0.5 for the contribution of both source images to make a new overlayed NEF and importing into Lr, in develop I see this:
White balance for the image looks fine, but the settings aren't right for the WB camera setting. Changing the WB from As Shot to Daylight shows how incorrect Lr has got the WB:
For comparison, Nikon's Capture NX-D gives the 'As Shot' WB settings Temp: 5209 Tint: 0 for both the original and the combined (overlayed) images. Changing settings to Direct Sunlight changes Temp: 5200 Tint: 0 in both cases without drastically changing the images' appearance.
The overlay camera function takes its settings from the first image selected for the overlay. So if overlaying two different images that were shot with different WB settings, the combined image has the WB settings for the first image. Capture NX-D reflects this - first image Daylight, second image Shade, the combined image has Temp: 5209 Tint: 0. First image Shade, second image Daylight, the combined image has Temp: 8006 Tint: 0. For Lr, either combined image has Temp: 2880 Tint: -119.