I don't have any of the new numbers I got this year. WTF.
The new contacts maybe could be retrieved from your online account or since last time you sync with the computer or cloud storage. Maybe some contacts could at the least be found from the phone record or last dialed numbers... not sure how the half would be missing...
Is this on a smartphone or a basic phone? Are the contacts associated with email address (Gmail?) and synced with the phone?
I have a smart phone and every time I add new contacts I do a back up to make sure they are saved using my phones back up feature. Mary