Stockpiling

It seems the tobacco companies knew about about last year's tobacco excise increase. From the financial statements:

Other customs and excise duties were $112m (12.2%) lower than forecast. Tobacco companies stockpiled imported product prior to the excise rate increase in April. This led to an increase in revenue at the end of the last financial year, but has also resulted in reduced revenue this year.

Wellington is a leaky place; it's not surprising that a massive tobacco excise increase wasn't kept secret.