Recently found a copy of the current 3rd Beta Monster Manual, and noticed a few things whilst checking it over.
First: The cover is not the only thing different from the 3rd Alpha, but the spine is as well, contrary to the info presented. Top is the 3rd Beta, bottom the 3rd Alpha.
If you'll notice, and thankfully the spine on the 3rdB is slightly faded to show this, the lettering on the title has been given a black outline as was done for the cover banner. Before, there was no border, and the background image merely showed through areas of the text as I have illustrated below, which kinda gives the illusion of outlines in spots.
Which brings me to point two, that the references to 'white outlines' on the descriptions of the 5th and 6th printings are incorrect. They are actually devoid of outlines as shown above. Check with a magnifying glass if you wish.
Third: The covers of both the 3rd Alpha and Beta I have are not textured, however my 2nd and 4th Alpha are. Any confirmation from the masses?