You've come to the right place, InformationPlease.
When a contractor receives the email invitation to add their information and submit the form, their information and PDF of the signed W-9 are added to their profile in your account.
Here's how to check:
Go to the Payroll menu and select Contractors.
Choose the contractor's name.
Click the Details tab to see the information and the Documents tab to look for a copy of the W-9.
If they haven't completed the data, you'll have the option to resend an invitation. However, if you do not have the option to resend the invite, the Personal details of your contractor have been completed. The resend email invite will only show if you haven't entered any personal information about the contractor.