Missing copies in Aleph

When a copy is not returned by a patron or is declared missing the
appropriate circulation area will add an item process status of MI
(missing) to the item record.

If the missing copy is replaced by either purchase or gift, technical services will create a new item record linked to the same holdings record for the replacement copy and, in the item record for the missing copy, change the item process status from MI to SU (suppressed).
The rationale is that patrons need to know if the only copy is missing. But if the missing copy is replaced they do not need to know that there is a missing copy in addition to an active copy.
Please note that the above applies to copies for the same edition/copies on the same record.