I’m afraid the ORB only records serials when an aircraft is delivered or when a mishap occurs. Several Wxxxx numbered aircraft are recorded in September: W3800, W3603 (both delivered Sept 7th), W3333 (lost Sept 7th), W3824 (delivered Sept 11th), W3449, W3637 (ground collision Sept 18th, W3893 (delivered Sept 26th).

I’d go along with VoyTech’s conjecture that aircraft ‘S’ could be W3893 due to it being delivered after P/O Whalen’s prang. However, it is just conjecture!