All a back-stamp means to me is that someone was obviously interested, taken by it. As to whether or not that they had swooned upon the sight of it is lost in time.
As for my American-Bulgarian 1c blue that you had determined to be a type II, I do wonder if P. V. Karaivanoff had determined it to be so as well, if that back-stamp is authentic. I have never seen any documentation for it. Accompanying papers do get lost, even before yet another comes into possession of a stamp.
In the end, if a back-stamp is unsupported by documentation, then it might as well have been stamped by Mickey Mouse, or Donald Duck. Then, I wish folks would not scribble onto the backs of stamps, at all.
As an aside, I would be blown away if I ever saw a back-stamp upon this one...
What, no comment upon the "Richter" stamp in question, and with its right side lost as well?