Good morning, @CD6 ...
I reviewed the "View Availability Dates" section of this Guide, What is the difference between assignment due date... - Canvas Community, and it sounds like you are doing everything correct, and the assignment should prevent students from submitting work to you. However, you said that students are re-submitting assignments to you beyond the date that you have set. The Guide I linked to really doesn't indicate this (from what I can tell), but I wonder since Canvas already knows that students have submitted the assignment once already (assuming here within the availability date range you've defined for the assignment), it is not counting re-submissions by the same students. What I mean is...maybe Canvas ignores the availability date for re-submissions?
It would be interesting to test this. If you had a separate "sandbox" course, you could create an assignment in that course with availability dates (for example, make an assignment that has a five-minute window where submissions can be accepted). Then, use the "test student" role to submit an assignment for the first time. Then, try to re-submit the assignment again...insuring that your re-submission is outside of the "until" availability date.
If you don't have a "sandbox" course, another option for you is to use your school's Canvas "test" environment...which is a separate environment where you can do any kind of testing you want without disturbing anything in your school's normal "production" environment (the environment that you are normally used to signing in to on a day-to-day basis). What is the Canvas test environment? and How do I access the Canvas test environment as an instructor? You could create an assignment in your course within the "test" environment just as I've described in the previous paragraph, and your students would never see it because you are in the "test" environment. Just be sure that when you are done testing things out that you sign out of the "test" environment completely before returning to your school's normal "production" environment.
Your other option would be to reach out to the folks at the Canvas Help Desk. They might be able to tell you specifics about submissions vs. re-submissions of Canvas assignments. How do I get help with Canvas as an instructor? - Canvas Community
I hope this information will be of some help to you. Please let Community members know if you have any other questions about this. Let us know if your testing confirmed anything. Take care...be well.
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