South Africa 1911 Cape "Twenty Stamp" Mark on Redirected Card

1911 "TWENTY STAMP" triangular bulk mail postmark on incoming postcard from Brazil subsequently redirected to Smithfield, OFS. Cape Town cds MY 16 11; at lower right the clear dated triangular postmark (Goldblatt Type P58) also of MY 16. This very scarce Cape of Good Hope postmark was used at the GPO for ONLY THE TOP ITEM on bundles of 20 or more cheap rate mail items and Goldblatt comments "NOT OFTEN SEEN". F-VF, scarce, a remarkable late use(special purpose?) in the Union period.