Marks Computation
The assistants are not responsible of the marks.
For every submission, all steps from previous stages are re-evaluated. For example, if you submit a tag for TC-3, the traces of TC-{1,2,3} will be computed. This gives you an opportunity to improve your previous steps and fix edge cases.
Your marks will be computed using your best traces (i.e. most likely your last step submission).
Warning
Even if failing the submission of a step is not a killer move for your project, having the moulinette test your code and send you traces is a good many of your predecessors could not have ever dreamed of. Use it wisely!