Can the first proxy see the IP address assigned to the user by the second proxy?

[hben2]

Is it correct to assume that the second proxy uses some form of NATing to assign end-user IP addresses different from the actual IP of the second proxy itself (ie the one that the first proxy would see and use to connect to it)?

If so, does the first proxy ever have visibility into the IP address assigned to a user on any granular connection/session basis?

Reason for asking is it seems the first proxy knowing both the user's original IP address and the one they end up assigned to seems like a vector for correlation by first proxy operators (Google) without collusion.

Thanks.