Having looked at my map, it seems that Carvin is a short way to the north west of Lens so while Sgt Herbert's claim appears in the Communique, Lt Barlow's claim (near Lens) must be considered a possible match also.
On page 9 of
Above The Trenches it is stated "Another difficulty arose; balloons claimed in 1917 and early 1918 were recorded on a separate form from used for claims against aircraft......40 Squadron, for instance, undertook some balloon 'strafes' in May 1917 which are listed in the RFC Communiques, but for which not all claim forms have been found, whilst those that do exist do not mention precise times...".
The lists of claims for both Barlow and Harrison in ATT show that the balloon claims appear in the squadron Operational Record Book; they do not appear in the RFC Communique, but this in itself proves nothing since the Communiques were not intended to be the official vehicle for claiming victories.
It all seems to depend upon who, at Squadron, Wing and Brigade level made the judgement call -"decisive" or "indecisive".
Graeme