It's already normalized to emissions per passenger-km, so I don't think the lifetime of the vehicle would skew it much unless it's efficiency changes over it's

It's already normalized to emissions per passenger-km, so I don't think the lifetime of the vehicle would skew it much unless it's efficiency changes over it's lifespan. Additionally, someone buying 4 or 5 new electric vehicles is not a problem. Unless they put the old car in a landfill, that will still replace 4 or 5 gas cars on the road as they are resold down the line. The carbon costs of producing them are already factored in!