@ C.S.Cameron,

Yes, the UUID of the ISO 9660 file system will contain the date that the iso file was created, but for released versions of Ubuntu all downloaded instances will have that UUID. Daily updates happen only with the daily iso files used for developing and testing. But that is not what I am thinking of.

I am thinking of what can be written into the 'writable' alias 'casper-rw' partition, if it exists.