Milly,
The Territorial Force re-numbering is useful for knowing which battalion of the Regiment that a soldier has signed his engagement with (in John Lovat Knight's case, the 5th), however, it does not necessarily determine the battalion that he was serving with. As you can see from the SDGW picture attached, John was serving with the 6th Bn when he was killed.
Please find below the blocks of Regimental numbers allocated to the 4th to the 7th Battalions of the Notts & Derby Regiment, Territorial Force:
200001 to 240000 4th Battalion Notts & Derby Regt
240001 to 265000 5th Battalion Notts & Derby Regt
265001 to 305000 6th Battalion Notts & Derby Regt
305001 to 330000 7th Battalion Notts & Derby Regt
The fact that John has changed battalions would suggest to me that something has happened, either wounded or become sick. On his recovery his Regimental Depot would have sent him back to the front to the Battalion which most needed him. It is likely to be after the battle of Loos, as before then the Territorials were contracted to only serve with their individual battalion of their regiment, and it took and it took an Army Council order, sanctioned from up high, to amend this. It is probably worth looking through the local press as this is full of useful information regarding casualties. You would be lucky to find this in the National Archives, as someone burned nearly all of the casualty records in the 1980s.
Both battalions were in the 46th North Midland Division. This division had a hard time at the battle of Loos, losing 3000 men in 10 minutes. After a tough time at Ypres, it was then in action again as the most northern Division of the British attack on the firsta day of the Battle of the Somme. It attacked at one of the, if not the worst positions, which was against a German fortified village that never fell - Gommecourt. Some of its men are buried in GOMMECOURT WOOD NEW CEMETERY.
Bill MacCormack, has written an excellent book about the 56th (London) Division (the Division in the southern part of the attack on Gommecourt), and has recently submitted his new book about the 46th (North Midland) Division for printing. I am sure it will be both informative and interesting. It may not mention John, but it will certainly mention a lot of the circumstances that he would have found himself in.
There is also a book about the 6th Bn by Clifford Houswey: Men of the High Peak: A History of the 1/6th Battalion the Sherwood Foresters 1914-18.
The 5th Battalion have a War Diary at the National Archives at Kew: WO 95/2695
As do the 6th Battalion: WO 95/2694
Hope this has been of use
Tom McC