MAURITANIA UPU ARCHIVE RECEIVING AUTHORITY SPECIMENS: 1941 Sun Yat Sen Fourth Issue: FULL SET of the February-issued denominations to the $10 and $20 top values. All in strips of three affixed to pieces of ledger page, without any specimen defacements, subsequently handstamped with large part 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. Minor imperfections, markedly superior condition to the norm. Unique and philatelically important group proving distribution of this issue in normal unused and undefaced state as specimens through the UPU. A wonderfully colourful array.