Elizabeth Matheson PAKA Pottery history

While looking at Elizabeth's pot markings I have come across some interesting history.
Elizabeth was born in 1890 and died in 1978.

She worked with metal artistically from the 1920's at Havelock North and moved on to clay in the 1930's.

In 1939/1940 she shared a Pottery stall with Olive Jones at the New Zealand Centennial Exhibition in Wellington.  They readily sold their wares and it was very successful.
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In 1953 Helen Mason bought Elizabeth's Matheson's diesel kiln, when Elizabeth was buying an electric kiln [Elizabeth was Helen's husband Malcolm Mason's aunt.]  I can't find a date for this!

Elizabeth made pottery from 1930 to 1975 and is considered to be one of our Pioneer Woman potters.

Elizabeth ran her pottery under the name PAKA Pottery.  
Paka in Maori relates to reddish brown.  Elizabeth only used terracotta clay.

Most of her work has the year made on it under the word PAKA.
Her mark is made up of E and M and this looks like an envelope with an extra line.
She also put a range of letters and dots on each of her pieces.
This is the mystery that we are trying to solve at present.
What do they refer to ?  That is the unanswered question.