Yeah, Yoda beat me to that answer. My guess is that the Final Five (really the first five?) are different but that those models do NOT have copies and that's because there is something "wrong" with them. Perhaps they were too sympathetic to humans (empathetic, perhaps), in ways the cylon powers that be didn't like.
Another explanation for Tigh/Adama might be Adama also being a cylon with implanted memories, but that would then mean Tigh has no one else in his life who remembers him younger -- which is a real stretch. Instead, this "final five rules are different" thing had to be added by the producers so that they could get around the obvious plot holes that would have developed when they chose characters to be cylons who were not cylons in their earlier envisionings.
Another explanation for Tigh/Adama might be Adama also being a cylon with implanted memories, but that would then mean Tigh has no one else in his life who remembers him younger -- which is a real stretch. Instead, this "final five rules are different" thing had to be added by the producers so that they could get around the obvious plot holes that would have developed when they chose characters to be cylons who were not cylons in their earlier envisionings.