what is use of consistent parameter='N' it doesn create a inconsistent dump

hi all

i have 17lacs record to create dump using exp and when exp is started i start updating certain fields on that same table

and while exp i put consistent='N'

still i dont get a incosnsitent dump as updates are not stored in the dump atleast some should hv been stored bcz i started
 the update the same time the dump was started

so why does consistent='N' not work??