If you are making changes for previous payruns, the Year to date (YTD) value that is reflected takes into account the amounts for the other payruns done prior to this. The system considers the YTD from the start of the year to the date when the payrun is ran, not the month the payrun is for.
For example: You have processed payruns from January to April. However in April, you realised that there is an error in January’s payrun. So you decide to run the January’s Payrun in the month of April. The YTD values will then include the values from the payruns since February - April.
To rectify this, you would need to delete all the affected payruns for the employee and reprocess them in month order.
How to process a payrun?