Quick search found this. Do a search on the term "month" on this file, and you will see lots of interesting data. Pages 14-18 are the most relevant pages.
Looks like approved shelf life for API is minimum 24 or 26 months under certain conditions (and based on which supplier it comes from), subject to a mandatory "re-test" (where it could be stored longer).
The clock then re-sets once the API is encapsulated.
One interesting note was that tested capsules were stored and remained stable up to 60 months under "long-term conditions" (proper temp and relative humidity). Not that this is the official expiration, just that this is what was tested.
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