Getting Outlook contacts from savefiles

I am currently working as a private support technician and today someone walked in with a Windows 10 PC that would not boot. After trying to repair Windows we decided to make a Backup from the whole hard drive and reinstall Windows. We reinstalled all his programs. Also Office. We set up the IMAP and SMTP Servers correctly but we are not sure if he was using Pop3 or IMAP we decided on setting up IMAP now. Everything fine. Now he has called us to complain that all his contacts are missing. So I went through the backup but can’t find any contacts. Where does Outlook safe contacts?

I tried
C:\Users\User\AppData\Roaming
C:\Users\User\Contacts (Some contacts but not all, the customer says he saved the contacts once manually there to back-up.)

Is are there any other location they could be?

Thanks for reading