Problems exporting at 300 ppi

To be clear about this: Export and Save For Web do not save at 72 ppi. They strip the resolution metadata entirely from the file. It has no ppi number.

72 is just the default value assigned by Photoshop when reopening the file.

Also, please teach your club that 300 pixel resolution by 1600-1200 and 72 pixel resolution 1600-1200 or 1000 pixel resolution by 1600-1200 are ALL the same! That so-called resolution value (300/72/1000 or anything else) is just a metadata tag. What is essential is the pixel dimensions which in this case are supposed to be 1600-1200, in length and height.

This super old article is no different today than when it was first published and should explain all this to your club:

http://digitaldog.net/files/Resolution.pdf

You're still using save as and not one of the export features? Any export feature, except save as, will change the ppi.

Try Image > Image size and set it up to 300 dpi (with resampling marked). You will notice an increase of the sizes, so it is important to correct sizes back to 1660/1200  before validate.

Then "save as" instead of export… and choose Jpeg or Png…

It should work

Don't use Export use Save (for PSD) / Save a Copy (for JPGs etc)