Mauritania 1906 Postage Due Help Needed

The postage due stamps of Mauritania from 1906 are the colonial issue surcharged with a T in a triangle. This set however is marked with the T only. The previous owner of this collection has written that this was used before the T in triangle came into use.
There is nothing mentioned about this in the Yvert catalogue and also a search on the internet gave no results.
Who can provide me with information about this stamps?

Maury doesn't mention these, so possibly an interesting creation by a stamp collector?

The strikes look extremely deliberate

The big T (from 1900) was used in France to tax letters.What the big T is doing on Mauritanian stamps I have no idea.
The T in a triangle; usage started in 1876 and ended in 1914..
The postmark is from Selibabi Mauritanie.There exists a big T in a triangle used in Mauritania.Could it be that the post office only had a big T(no triangle) handstamp available? Possible; selibabi was a very remote place at that time At best I would think that these were philatelic souvenirs from that time.