According to BW, “The first recorded example of this stamp was discovered in 1922. Four examples can be confirmed. These comprise two mint and two used examples, of which one of each are in the Royal collection.”
The 6d bi-colour (BW) D86 with double lined A watermark, on thick paper exists as perf 12.2 x 12.4 comb, or the rare (BW) D87 perf 11 singe line. According to BW, there were 4 printings, made between June 1909 and Jan 1912, which comprised 360,000 stamps, or after spoilage, a total of 355,800 stamps.
The double lined A watermark on thin paper was first used for postage dues in June 1913 – ½d (SG D76) initially with perf 12.4 single line, and a run of perf 11 in July 1914 for the ½d and 1d (SG D77 and D78). This paper continued to be used until the end of 1921 when it was succeeded by the multiple C of A watermarked paper.
There was no issue of the 6d on thin paper (saving any argument as to what our particular stamp is). It seems that there must have been the odd sheet of the double lined A watermarked thick paper caught up in the perf 11 printings, which resulted in the 1d SG D74, and 2d SG D74a.
Of the 1d thick paper perf 11 BW states, “The variety is reported in the philatelic literature in December 1912 but used examples date from late 1914 and early 1915 (Qld, Adelaide, Melbourne etc cancels). Of the 2d, only two examples have been discovered. One is unused without gum (discovered in 1972) and the other is pen cancelled and undated (discovered in 1988).”