Most breed associations got ahead of this years ago by having a separare record data field for Registration Number, Herd ID, and Official ID.  Most breed associations set both Registration Number and Official ID to the EID number, then when the Offcial ID is lost, a new EID is installed and Official ID is updated to reflect new EID number while Registration Number remains unchanged.  This allows the current EID to always point to the same animal record (Registration Number) and the Herd ID can refer to the Tag Number.