Currently, the pre-defined "expiry date" filed is just intended to be used for sample alerts. If an alert is dismissed, not only the alert is silenced but the entire information of "expiry date" is deleted from the system.
It would be helpful, if that information is still kept (including the automated calculation how long a sample is already expired) even when the related alert is dismissed.
Maybe a good option is to separate setting of "expiry date" from the alert menu to an extra button and in the alert menu just allow ticking if an alert on expiry date shall be generated or not.
In my opinion, such a system behavior would be more intuitive and more consistent to the other alerts behavior (e.g. Setting an alert on sample volume does not delete the volume entry when the alert is being dismissed).
Please, consider making this small but useful change to the system.