Robin,
I recalled an SF Edge Special being sold at an auction at Olympia a number of years ago, though I cannot find the catalogue now. However I looked through back issues of The Automobile and found that it was at Brooks sale on 2 Dec 1996. "An aluminium finished AC S.F.Edge Special Sports 2-seater dating from 1924 sold for £9,000 - a bargain. This was a very nice example...." (Automobile Feb '97 Page 37"
In the same issue David Howard has an advert on page 87 for a "1924 AC S.F. Edge Special Sports 6-cylinder 2-seater with dickey. Finished in aluminium and dark green with matching leather. Shipped new to Australia as Works demonstrator. Fitted triple carbs and sold new with 80mph Brooklands guarantee." Possibly this is the same car. From the photo in David's advert the registration number of his car is SV 4587.
I am not sure whether this might be chassis no 13335 which is listed in the register as ex works 1926, but does not quote a registration number.
Hope this might help put you on the track of this example.
John Davison