Why do the amounts of tar and nicotine content reported by cigarette manufacturers not accurately reflect the amounts of these substances ingested by smokers

This is due to the manufacturers doing the analytical measurement mechanically. This measurement is done after the cigarette production.

When the cigarettes are lit up and smoked, the nicotine content and tar reduces due to part of it being evaporated into the air. This is the reason why cigarettes that are chewed have a higher percentage of nicotine and tar ingested.

i believe it is the last one. im sorry if im wrong!