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

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, represent...

Based on data coming from the API only, how can one know whether an assignment was created using an old or a new gradebook?

Based on data coming from the API only, how can one know whether an assignment was created using an old or a new gradebook? 

How to find out when a grade has been released ?

Now that Muted/Unmuted field is depreciated in the database, how I can find out if a grade is visible to a student based on the data only ? More specifically, how can I know when a submission's grade...