Keith;
This is what I've found so far.
Reference: Attached Image (6 AA Div Formation Sign Used has an example)
Fig. 1 - According to what I've found, from a War Office letter of 12 April, 1940 - AA Units within AA Command used a oval or ellipse AoS patch, divided vertically, with no Unit identifing number serial, starting in 1940.
Fig. 2 - According to the 1942 instructions, the only change was that the oval or ellipse AoS patch was divided horizontally, with still no Unit identifing number serial.
Fig. 3 - According to the 1943 instructions, only AA Units within AA Command Mobile Reserve were to carry Unit identifing serials, which were allotted by the G.O.C. C-in-C AA Command (after Nov 1943), also, the oval or ellipse AoS patch was still used (not changed to the square pattern used by the Field Army)
Fig. 4 - The markings found on the LAAT. I haven't found any reference for 1944, nor any reference to the Unit serial '6' yet, but the AoS patch and Unit serial could date from then.
That's about it for now Keith, still looking.
Cheers
