For purposes of my own data base on DSO awards I should also like to know. It is evident that no citation was published then or thereafter. One would therefore have to look for a recommendation and for this one must resort to PRO documents in the AIR 1 series. Assuming the documents still exist, they are most likely in AIR 1/1155/204/5/2441. I suggest it because, in 1999, when looking for the citation to
Redford Mulock's Bar to DSO, I consulted this file. I did not find a recommendation for the Bar, but did find a recommendation to a DSC which MIGHT have been upgraded to the Bar to DSO.
IF the file yields a recommendation for the award to Dallas, it might also have recommendations for others, viz: Wing Captain Robert Hamilton Clark-Hall and Wing Commander Henry Meyrick Cave-Brown-Cave. I would be equally interested to hear about their documentation.