It’s not an accounting or numbers question.

Commander-in-Chief of Fighter Command, Air Chief Marshal Sir Hugh Dowding, who once was so reluctant to allow Polish pilots into battle, summarised their contribution in probably the most telling way:

‘Had it not been for the magnificent work of the Polish squadrons and their unsurpassed gallantry, I hesitate to say that the outcome of battle would have been the same’.

Documentary about Sq. 303: https://www.youtube.com/watch?v=rgTLwN-SysI