Three rules explain most of what you will observe when connecting accounts.
One account, one organization
An external social account can be attached to only one organization. The same Instagram account cannot be connected to two organizations at once. Agencies: put each client's accounts in that client's organization from the start.
Plans gate platform access
Access to each platform is controlled by the organization's entitlements. A plan without X access cannot connect or publish to X. Each connected account counts as a source in billing.
The account outlives the person who connected it
The social account belongs to the organization. Each member's authorization is a separate credential with its own tokens and scopes, so several members can authorize the same account. As long as one valid grant exists, the account keeps working. When the last valid grant expires, the account shows reauthorization_required until someone reconnects it.