Are we confident that this preface was actually written by Orwell? Is there testimony from that time that he had written such a preface? Because it seems to me

Are we confident that this preface was actually written by Orwell? Is there testimony from that time that he had written such a preface? Because it seems to me that the propagandistic exploitative value of 'finding' and publishing a preface supposedly from Orwell would be very high and that this preface could well be a fraud.