What are the different events that can populate submission_dim.posted_at field (obtained via the API) ?

Community Novice

I initially thought that submissions' posted_at timestamps would either be the same as the graded_at values, or some later date, identical for all submissions linked to the same assignment, representing the date-time when all grades are released to students. But I have found several cases where the submission_dim.posted_at date value is before any submission is even graded. I have also find cases where submissions have posted_at values over a year after these have been graded... Hence I am trying to understand the different types of event that can lead to populate the posted_at field.