What is the serial number of the very first Spitfire to enter RAF service?

From the Jeffrey Quill book ‘Birth of a legend’
He says that…..

K9788… (2nd production a/c) accepted by Air Member for Development and production dept on 17 July 1938 (but actually delivered to RR Hucknall).

K9792… delivered to CFS Upavon 29 July 1938 (accepted by F/L George Stainforth of Schneider fame )

K9789… J Quill delivered this a/c to 19 sqdn Duxford on 4 Aug 1938

So I guess depending on how the a/c serial numbers were allocated in those days,the first spit into sqdn service may have been the 3rd production a/c
K9789.