2nd Map Ref query

[TEW]

I'm asking for help with a Map reference look up. I have some Army Form pads C 2121 and one dated 12/4/1917 while the 2/5th KOYLI were billeted at ERVILLERS in Reserve. The relevant C2121 says;

"Right Platoon Commander reports 9.15 am AAA. Captured first objective 9.2 am. AAA. enemy estimated at 250 retreating at 9.10 am N.N.E. from about B.17.c.5.4. AAA. Message ends

It makes no sense for this date and Battalion as there were away from the front at this time. It is signed by my grandfather and dated by him with time and location (Field). None of the maps held on my computer show any B squares. I realise I don't have the actual map sheet number but his general movements for this time were Beaumont Hamel, Miraumont, Achiet Le Petit, Bois d' Holland, Mailly Maillet, Courcelles Le Comte, Sapignies, Ervillers. The Battalion moved off to Bullecourt on 16/4/1917.

If I could get any locations for B.17.c.5.4 I hope to work out a likely date and set of circumstances. As I have other C2121's that mention lots of activity around 9.0-9.30am but the date for those is 3/5/1917 (2nd Bullecourt) and no B square in sight.

Any suggestions gratefully received

TW