Uniquely identifying a grade book item for grade pass back

Hi,

I'm implementing my first grade pass back from an External LTI which I've developed.  Based on my use case, my plan is to associate a canvas user_id with the lis_result_sourcedid as well as the lis_outcome_service_url when the user initiates a launch of an assignment through Canvas; this information will then be saved in my database.  Then, at a future point in time, I'll run a CRON job to actually pass back the score to the gradebook.

I've been able to perform this action on a one time basis.  However, I would like to verify that this unique combination of canvas user_id, lis_result_sourcedid, and lis_outcome_service_url never changes for a particular assignment.  In other words, if a student re-logs in at a future date, creating a new instance, can it be guaranteed that my post back to Canvas will still hit the same gradebook entry?

Thanks so much!

-Eric