Is there a way to sync missing data into Salesforce? (SFDC)

We would recommend performing a full re-sync of your data as that should push all missing data over from Recurly to SFDC. 
To do this:

1. Go to the Recurly Admin tab and select "Sync Settings."
2. Click "Edit"
3. Scroll down to Last Sync and enter a year in the date field back to a date of your choosing and hit Save.