ODME modified plan resets all mailboxes to 'Created'

Hi, we have corrected 2 email addresses in a plan of 50 users (48 had Completed).  After saving the changes, now all 50 mailboxes look like they will start again (Status 'Created' and 0 items/percent).  Why does this happen and when we start it, what will happen?  i.e. will it consume licenses again for all 50 mailboxes? will it re-sync all mailboxes again from the beginning or just transfer updated items?  If it does restart, will it duplicate items in the target?

It seems to work in a convoluted way - why not just sync the mailboxes then do an incremental sync daily until we hit a 'Complete Plan' button?  I assumed this is how it would work, possibly incorrectly as I've also read that I should be migrating based on date ranges and that it is 'recommended', however this is not mentioned at all in the documentation.

If it does turn out we have duplicated items and we decide to delete the target data and re-migrate, can I delete all the current plans put all the users into a new plan and ODME will recognize they are licensed and do an incremental sync?

It's a shame this information and recommended approach are not covered in detail in the user guide.

Thanks, Simon