The commoner error "stop after exhibition" seen better in pairs with and without stop. Long ago, I bought a set with a lot of these but in singles.
In part 1, I alluded to the possibility that the errors were manufactured. However, there is letter from the postmaster general of the time, CFN Wade dated 4th July 1922, that stated the errors were not intentional and the rush to get the stamps ready prevented their discovery and subsequent sale. He also stated the following numbers for the " stop after exhibition" stamps: 1c - 160, 2c&12c - 550, 3c to 24c - 275, 25c&50c - 104. This error was said to occur on the 7th stamp of every second row.
Reference: The stamps and postal history of NB part 3.