--- You wrote:
How long will primary IAEA standards last if we use them every day?
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You can develop your own in house carbonate standards with different values if you run very often.

As it is we use about 0.2 mg of carbonate standard per sample on the gas bench so for the IAEA standards you could run a bottle of 0.4g ($181) about 2000 times and if you run 2 replicates per day that would be 1000 days. So you might just have enough to last the three years between ordering periods.