Enabling Resource Management from Existing Smartsheet

Hi - I have a pretty basic sheet in Smartsheet with contractors' names and dates they're available for work. It changes from week to week and they go in and update it after they receive an automated Smartsheet form reminder via email to update it.

We're new to Resource Management and in trying to enable RM with this sheet, I've gotten the dates and some names to transfer over to RM successfully, but not all of the names. I'm at a loss as to why not all of the names are transferred. The email addresses are the same in RM and Smartsheet, and the names are spelled the same. Why might the Assigned Resource column only pick up some names but not others? I've done a copy-and-paste of the email addresses as well as hand typing them out and it still won't populate. I've tried to type them in fresh in new, unused cells, and that doesn't work, either. There are no hidden columns and I'm the only person who has used the sheet all day.

Thoughts?

Thanks!