Hi,
As there is no history on how the quntity is reduced from 4500 to 0, I think this reducntion was made by goods movement but the customization of making history for this activity has not been done in your system. Please see note 1875219 on how to make it happen, especially for the section of transaction OMP4 and field 'History Dur. Reductn', the field need to be selected if you'd like to make history for the reduction by goods movements.
Best Regards.
Leon.