As part of our data health we remove records from Eloqua for a number of reasons (inactivity, unsubscribe, etc). Once removed the contacts are no longer in the contact table and can not be pulled into segments via filters.
We needed an overall current unsubscription list overtime for an upcoming system integration.
If you are trying to access this same information it can be found under Setup > PowerTools (Screen shot from our specific license of Eloqua, thx for heads up Vickie Le Sellin that some licenses may have different options.)
Then Select Overall Current Unsubscription List (All Time)
This will allow you to download a spreadsheet containing all of the data. Note: Records removed from the system will likely only contain the email address and removal date. Unsubscribes still in the contact table provide greater detail.
HIGH FIVE to @Michael Green on my team for figuring this out. I couldn't find it so I wanted to document here for next time.
cc Leyla Farah -