Serial 78 for the LAA Regt in Chart 1 for Gds Armd Div is evidently a typo for 73. Other discrepancies between the two charts are also problematic. The Counter Mortar Battery (Serial 78) in the OOB of Armd Divs comes from Hodges & Taylor. I have no idea when or even whether this was actually implemented. It is probable that it did not exist for the whole of the NWE campaign.