Tanganyika 1916 NF Ovpts Mauritania UPU Archive Specimens

MAURITANIA UPU ARCHIVE RECEIVING AUTHORITY SPECIMENS: 1916 NF OVPTS: Full Set comprising ½d, 1d, 3d, 4d & 1/- (SG N1-N5) ovptd SPECIMEN. Stamps all in multiples of three affixed to portion 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 for this popular issue.