CA5023 Canada O.H.M.S. Official Letter Posted in Hong Kong 1951

Postmarked: Hong Kong, 24 JA 1951.
This cover has a fascinating story as we make it out.  It started in Hong Kong O.H.M.S. without postage.  Upon Arrival in Canada, a purple postage due hand-stamp went on it.  Later it was covered by an O.H.M.S. 50¢ perforated stamp # O272.  Notice that there are perforations missing in each of the letters.
Small tears at top.  Stamp is slightly damaged.