Sorry but here comes a lot of pics and long answer...
I agree that B. caudalis can be so variable, even if 2 are found under the same rock1 there is a good chance of a difference.
Although one can generally identify the greater area from which it came. The most variable ones in my opinion come from the Namib plateau.
Here are pics (from a friend) of B. caudalis from different areas of the Namib Plateau (Windhoek, Karabib, Omaruru, etc).
Here is an Absolutely Amazing Amelanistic B. caudalis from closer to the coast...Usakos I think.
B. caudalis from around Etosha Pan in Namibia have always been known to be nice, here are three young specimens.
Also In my experience the ones from the area around Aus in southern Namibia are always drab brown and almost patternless. I cant find the pics I had.
Below images of Horned Adders from Namaqualand, South Africa. In my experience are usually bright orange or reddish brown, sometimes with nice gunmetal blue markings.
B. caudalis form Messina, Northern Province, SA....very nice!
Onto Bitis cornuta. I have found them to be similar across the range except for those from the coastal regions of South Africa (Port Nolloth, Kleinsee, Hondeklipbaai) tend to be more reddish/brown (or have red/brown flecks) in them. Nice boldy marked ones resembling B. albanica are found in the Knersvlakte region of Souther Namaqualand.
Also there is a population of 'ghost phase' B. cornuta from an undisclosed locality near Luderitz, Namibia.
Coastal B. cornuta (Port Nolloth, Kleinsee)
Standard cornuta from Namaqualand (Springbok)
Boldly marked B. cornuta from Namaqualand Knersvlakte (Vanrhynsdorp)
standard Luderitz B. cornuta
[img]http://www.sareptiles.co.za/gallery/albums/userpics/10007/Bitis_cornuta_luderitz4.jpg[/img]
'Ghost Phase' B. cornuta from near Luderitz:
Desert Mountain Adders. They seem to be the similar across the range except I once found a DOR B. xeropaga in at Aggeneys (near Poffadder) that was mostly dull reddish with feint markings (A little like B. rubida) I dont have a pic though.
A friend of mine also claims that B. xeropaga are sexually dimorpihic
Here is a picture of a bold male B. xeropaga mating with a duller female. Apparently most females are like this.
Male combat in B. xeropaga
CB B. xeropaga
Berg Adders - B. atropos. Unfortunatley, I dont have many pics except for 2 from the south western Cape.