Ascension 1922 Mauritania Archive Specimens, Unique

MAURITANIA UPU ARCHIVE RECEIVING AUTHORITY SPECIMENS: 1922 KGV ½d - 3/- (SG 1-9). FULL SET of regular UPU SPECIMENS overprinted in the usual manner mostly in strips of three affixed to portions of ledger page and additionally 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. Odd minor imperfections as usual for these. A unique & philatelically important group, a colourful array!