In case it's of interest to others, I've recently come across "The President who lost his face" by Wolfgang Baldus in Germany from 2012
He's written about the defaced postcards and envelopes featuring Pres Johnson
I found it a fascinating read (24 pages), full of useful information about how these came about, lots of illustrations etc.
Wolfgang has put together details of around 60 cards/covers in his possession
It's a very useful addition to Henry Chandla's article in LPS April 2013 for those interested
Amongst other things Wolfgang argues that the items weren't defaced because Pres Johnson had run off with the Treasury money (as Rogers et al report) but rather that Johnson didn't like the way he looked in the vignette and ordered them erased!
Cost me 15 Euros direct from Wolfgang (I'm not on commission!)