Queries :: Update Query To Add Data To Table NOT Overwrite

I have a table that is updated from an update query which gets its data from a table, which gets its data from a form. I have set the query to only update the current record, this is done by a macro when the user exits the input box. The problem arises when a user goes to visit past record, I would like it to not overwrite the old data with the new data. If the query was only allowed to ADD data and not overwrite then this would fix the problem!

My SQL code is as follows:

UPDATE [Run Info], [Sieve Weights] SET [Run Info].[315 Tare] = [Sieve Weights]![315 Tare], [Run Info].[250 Tare] = [Sieve Weights]![250 Tare], [Run Info].[200 Tare] = [Sieve Weights]![200 Tare], [Run Info].[160 Tare] = [Sieve Weights]![160 Tare], [Run Info].[100 Tare] = [Sieve Weights]![100 Tare], [Run Info].[75 Tare] = [Sieve Weights]![75 Tare], [Run Info].[50 Tare] = [Sieve Weights]![50 Tare], [Run Info].[BD Tube Tare] = [Sieve Weights]![BD Tube]
WHERE ((([Forms]![1L Input form]![ID No])=[Run Info]![ID No]));