The UCI is assigned to an individual, and if the application is successful, becomes the permanent ID for any transaction with CIC. And sooner, it becomes the ID on the PR card issued to the individual. So natural lang na each individual included in the application has their own UCI.This seems to be true only for PNP applications - I have seen cases - mostly in the family/spouse sponsorship, wherein the UCI issued to the sponsored member can be used to see the application. But for PNP applications, this is typical - as you are the applicant (note in all forms - you are the declared applicant) and all others are termed included in the application and are either dependents or spouse/s. As far as CIC is concerned, it is only you who as an active application file with them.
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