St Lucia 1967 QEII Postage Due Statehood Black Overprint 16c Pair UM Mint Trial?

Queen Elizabeth II Postage Due Statehood overprint 16c pair mint. Overprinted in black which was noted as a trial surcharge - am very unsure on the status of these. Unmounted mint.

Year : 1967

Reign : Queen Elizabeth II

Catalogue No : SG footnote

Condition : Unmounted Mint

Price : highest bid