C02 does not get into green coffee. I believe you are thinking of Oxygen.

Carbon Dioxide is too small and repelled by the 10-13% h20 within the bean.

Co2 leaves roasted coffee and the oils (lipids) create a bitter taste.

After O2 invades green coffee it produces - Aldehydes which are not bitter, they have a papery flavor like a formaldehyde paper mill.

Green beans depending on their density only last about 8 months.

Now there are ways around it: store it in a tote and flush it with xenon.

Also: moisture is important for the preservation of green coffee flavor. Do not keep them dry. They will 'fuzzy' up and lose their ideal h20%

Ideally they are kept at 60f and at a perfect 50% humidity so they do not gain or lose H20