There is no reason why you can’t do that.
Just watch out for the posting date of every invoice, GL, payment entry, etc…
Also figure out naming series for all documents as you don’t want the “catching-up” data to have higher series than the current ones (as they date older).
Edit: remember to close your financial statements for previous years.
For manual import of old data, this might help you make the process faster. Otherwise use the data import tool whenever possible.