The only thing I can find is 2015 version which lists 4 screws that need to be drilled. The 2019 package has changed so only 2 screws are
provided but no hints at whether you drill front or rear. Does anyone have the newer instructions?

 

Found a video with the newer parts. No drilling required. And a big thank you to the technician who posted it. Probably could have figured it out with the old instructions and newer guards but it made it easy. And no thanks to Lexus - why in the world can't you drop a simple sheet of paper in the box with instructions or post them. They seem to guard these like nuclear secrets.

 

The overpriced genuine Lexus mudflaps were not yet available for the 2019 NX in early 2019, so I purchased inexpensive ones from Amazon ($30 for all 4). Granted, the quality and fit were not as good as the Lexus ones (particularly the rear fit), but good enough for me. They are still in as-new condition after more than 2 years of use and 2 New England winters.

These also did not include instructions, so I created my own. While these instructions will not match your mudflaps, they should provide guidance regarding what kind of fasteners to use and where the mounting locations are on the vehicle. Individual "push pin" clips can be purchased at Lowes/Home_Depot, or assortments are available from Amazon for $5 to $10.

 

I agree that I could have figured it out. The problem was I had no desire to drill a hole and then discover it was not correct. They reduced the number drill holes from 4 to 2 from 2015 to 2019.