[4] Beginning with the 1907–08 season, the competition was decided by challenge matches among Auckland, Wellington, Canterbury, Otago and, on two occasions, Hawke's Bay.

[5] A proposal in 1912 that the Shield should be decided by an inter-provincial tournament rather than by the challenge system was rejected as impracticable at the time.

[6] However, starting with the 1921–22 season, the four principal teams (minus Hawke's Bay, which lost first-class status) played each other in a single round-robin series of matches.

In latter years the format was experimented with, introducing a shorter second round, various bonus points systems, and eventually a knockout final.

New Zealand Cricket stated that the naming rights were no longer for sale and that the competition would henceforth be known as the Plunket Shield.

[10] The holders of the shield during its "challenge match" period to 1921 were: From the 1921–22 season the competition has been run on a round robin format.