Just to clear the air a bit here about the IP check tool, almost all home internet connections use what is called "dynamic IP addresses". Your internet provider has a pool of IPs and you are randomly assigned one and it changes frequently (several times a week). Try doing regular IP address checks on your own account over time and I'm sure you will see lots of changes.

Most businesses and power-users that have high end internet connections have "dedicated IP adrresses", and their IP is theirs alone. Connecting at a Starbucks for example, your IP will be one of only a few that the specific Starbucks location uses. Others using that same Starbucks will sometimes use the same IP you previously used.

The IP check tool is useful if someone is posting with the same IP and multiple identities during a very short period of time (ie; hours or days), but if a different user had the same IP a year ago it is really a stretch to accuse them of running multiple identities.