Sherwood Forester transfered to 13th RIR

[TrooperKerry]

Looking into my local WW1 roll of honour (Nottinghamshire) and notice that a number of Foresters, mostly 11th Service Battalion transferred to the 13th Royal Irish Rifles.  Looks like post Somme July 1916 & some listed in the war diaries of the 13th RIR wounded killed at Messines 1917. Serial numbers all around 43117 . Cant see in the Foresters WD where any significant number transferred or why and the same in RIR WD. The serial numbers don't seem to be significant either. Does anyone have any idea's is it just a random occurrences!