For a portal that lists all records in the table, set up a relationship between two occurrences (instances in your terms) matching by any two fields you care to select, then double click the relationship line and change the = operator to the cartesian join operator: X. This will match any record on one side of the relationship to all records on the other side.
Brilliant. That appears to have done the trick. I thank you sincerely for your help. Who knows how long that would have taken me to figure out on my own!