So obviously Nip and Nipperkin aren't the same
The nipperkin is a unit of measurement of volume, equal to one-half of a quarter-gill, one-eighth of a gill, or one thirty-second of an English pint. In other estimations, one nip (an abbreviation that originated in 1796) is either one-third of a pint, or any amount less than or equal to half a pint.[1]

but some brewers also bottled in nip (1/3-pint) ( Both from wiki)