Kevin,
Last count I have is there are 11 security code versions. Some have different codes or no code on each side. Here is a list.

Egypt / blank
Egypt / Egypt
Nile / Nile
Luxor / Circus Circus
Luxor / Luxor
blank / blank
Tut / Tut
Circus Circus / Circus Circus
Pyramid / Pyramid
Pyramid / Nile
Nile / Luxor

I have all but the last two.
Paul