Thanks for the interesting reference Ron.
The four Higlet articles were all worth reading and I'd not come across them before.
I see the original article showed ten examples and the author of the blog has added the other ones which are in colour.
I had a quick look at my other catalogues.
Pulko has a full listing for 1906 for three of these stamps, the three values from the 1905 issue.
This doesn't mention different overprint types but does note that they can also be found in blue and red.
The image given is similar to Higlet's Galata types.
SG notes that the same three 1905 values were handstamped with "T" to act as postage due stamps.
I suspect that there will be both forgeries and bogus stamps.
I don't see how Rafa's examples could be genuine given their date of issue but they are handsome stamps.