If you reformatted the hard drive and don't have a backup then there is nothing you can do with regard to your old list, other than rebuild with use.
If you do have the backup, the 'To:' list is stored separately in a file. In Office versions to 2007, Outlook.NK2 which should be in the same folder as your Outlook data file and is not synchronised with Contacts.
In Office versions 2010 and 2013 the list is stored ina dat format file. For more information see
http://www.nirsoft.net/utils/outlook...ize_limit.html
You can copy your Contacts to this list using
http://www.nirsoft.net/utils/outlook_nk2_edit.html