Hey Pete,

One comment about UV markings - some UV marks are faint...
Yet if both of your chips and Irwin's chips don't have an UV mark on them, then this (IMO) would make yet another variety! <VBG>

Another thought, the arcade at the Hard Rock has some strong UV lights, you can walk in there with some Hard Rock chips and see the UV H&C easily. Something that you might try - check a Hard Rock chip with your UV Light, if you don't see a UV H&C, then take the chips (a Hard Rock and the Dunes) to the Hard Rock (on your next chip trip), and walk into the arcade to see if you can see the UV Markings...
You may want to take them to the Hard Rock Arcade anyway, since the Orange UV Marks are harder to see than the green UV marks (which are on the Hard Rock chips...)...

Let me know what you find out...

Regards,

Dick