Aaahaa, the penny drops! Thanks for the info, Dog, I hadn't quite put 2 and 2 together there and upon further reading it clears things up a little.
However, even taking into account the "acclimatised when local time is +/- 2 hours" rule, I believe there are still plenty of trips around featuring four consecutive early starts, which still exceeds the CAA guidline.
Anyone else had any proper cases of 5-6 earlies in a row?