Candidate applies by himself on a requisition, is referral possible afterwards ?

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 Candidate applies by himself on a requisition, is referral possible afterwards ?

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Hello,

I have a candidate who applied by himself on a requisition, on the external career site.

From what I read and understand in Doc ID 1628435.1 :

Submission ownership = If the candidate applies himself on a requisition the Referral tab remains empty (even if there is a referrer on the general profile).

But in my example candidate, a few weeks later an employee referred him and was displayed in the submission Referral tab of this candidate.

I thought that when a candidate applied first by himself, no referrals were possible afterwards ? Did I not understand correctly ?