Hi Mei

There is some documentation on Certifications that explains the concepts with examples.

When the recertification window opens all learning paths will be reset - the learner will still have twelve month to recertify but the recertification will be open two months before expiry of primary certification.

The due date won't need to be manually reset this will automatically adjusted depending on settings.

The due date is the actual due date rather than the assigned due date as these may differ as described here

regards