The only time I use save for web is to save animated GIF because Save for Web save all Jpes set to 72DPI I Don USE s4w...
Did to see my append that you can undo Place scaling above....
It also possible to undo Photoshop's Place scaling with a simple calculation. Divide the image layer's original dpi by the document's dpi here there are three layer that did not start at 300dpi. two started out as 74dpi image file the other a 500dpi image file. 72/300=.24 = 24% the other 500/300=1.66666 = 166.66%
all you need do is change the associated layer's image transform width and height scale from 100% to the calculated percents
