Tanganyika 1917 KGV Mauritania UPU Archive Specimens

MAURITANIA UPU ARCHIVE RECEIVING AUTHORITY SPECIMENS: 1917-21: KGV values comprising 25c, 75c & 5R all ovptd SPECIMEN. Stamps all in strips of three affixed to two portions of ledger page and handstamped with 3-line "SPECIMEN / COLLECTION / MAURITANIE" in red-purple. Sent from the UPU in Berne to the Mauritania Post Office where they were affixed to the ledger page and tied by the Mauritania handstamp. Condition with imperfections as usual for these, a nonetheless unique and philatelically important group.