How far back can you go to restore contacts/

I'm not sure how far back but if your contacts were synced to iCloud, try the following. Use a computer internet browser and log into www.icloud.com and then click Account Settings near the top middle of that screen. Then in the Advances section of the next screen, click Restore Contacts and see what dates are available to restore.

If you synced contacts to iCloud see this Apple link ➡️ Restore contacts, calendars, bookmarks, and more using iCloud.com - Apple Support

If your contacts sync with some other service (e.g., MS Exchange, gmail, AOL, Yahoo, etc) see what recovery services are available from that provider.