Unless you actively pay attention it's very easy to be logged into some Google service without noticing. At least I wouldn't be surprised if chrome background services kept me logged into my work Google Mail account and kept tracking my IP.

The biggest question is how meaningful the IP alone is. I don't know if VPNs assign people individual IP-adresses or if there's some kind of NAT in use where people share an IP with translated ports. If the information is "there's this individual VPN-user and we need to connect them to a name" then you shouldn't use (the same) VPN for everything, but if it's just "there's another request from the same VPN" then it's fine.