That’s likely what’s happened. The year end tool will pick up everything from the last year end date until the next one that you’ve selected, based on what’s entered in the Company Settings (there’s more info on this here).
Check the year end date in the company settings, and if needed, change it back a year and run the year end tool. Providing there are no locks on the account, then this should be all OK. Running the tool itself will lock down the entries however to prevent them from being changed.
Hope that helps!