It sounds as if the 3400 and 4500 refer to the wattages of the upper and lower elements, which will never be on at the same time if the upper thermostat is wired correctly.
The thermostat contact resistance should be a small fraction of an ohm.
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Starting to put more together here - 12 ohms is getting somewhat close to resistance of a 3400 watt 240 volt element, I think there is some terminology issues going on. I don't know if the cold vs hot resistance changes much with these elements either, but if he tested something at 12 ohms, my guess is it was likely across an element - and it probably is good.
Add, I don't think 3400 is a common 240 volt rating though, 3800 seems to be a standard rating. 3400 is about what a 4500 watt element will run at if connected to 208 volts though, so what he is seeing as 3400 and 4500 is probably the watt rating at 208 and 240 volts respectively.