When working with relationship imports in Importacular (whether Individual or organisation), there are a few things to check if your existing relationships were not updated as you expected.
1) Start by checking the appropriate Criteria Sets. Relationships are matched to existing relationships in the Raiser's Edge by Relationship Criteria Sets - one for Individuals and another for Organisations. If you are working with a Constituent Relationship, both the Constituent Criteria Sets and the Relationship Criteria Sets will be applicable (the first will match the Constituent record and the second will match the Relationship)
2) Next, if your Criteria Sets are not the issue, if you are working with a constituent relationship, check to see if it is reciprocated in the Raiser's Edge. Existing relationships are only picked up when the relationship is reciprocated.
3) Check your Area Settings for your relationship mapping to ensure that they are set as you would like them to function. For information on Individual Relationship, see this section of the User Guide. For Organisation Relationships, see this section of the User Guide.