An interesting topic, bronto ... While myself, I would strongly lean towards the use of a regular expression or unpack statement for its simplicity in this task, I would add that the serial number of a DNS zone file does not necessarily have to follow this format - See RFC1035. The serial number of a DNS zone file is an unsigned 32-bit number which is wrapped for zone versioning - It does not have to take account of current date stamps as suggested, indeed, even the simple increment of a zone files' serial number would be sufficient for updates.

I add this point as more often than not, it is administrative policy moreso than technical requirements which adds the complexity of administrative problems :-)