1999 One Dollar Varieties
The introduction of the new and larger portrait of Queen Elizabeth II by Ian Rank-Broadley in 1999 necessitated some design changes part-way through production of 1999-dated $1 coins, and as a result there were two different obverses used for both circulating and commemorative coins. The small portrait/head obverse has the legend text far from the rim and the medium portrait/head has the legend text close to the rim. A third obverse - the large portrait/head - has also been reported, with the legend text almost touching the rim (Andrews, http://thesandpit.net/index.php?option=1999dollar). The only difference between it and the medium portrait/head is the length/height of the legend text letters: close examination indicates that it is actually the same variety as the medium portrait/head but with strike doubling on the legend text which resulted in slightly taller letters.
Both varieties can be found in circulation on the International Year of the Older Persons dollar with the small portrait/head being much less common, accounting for approximately 3.8% of circulating 1999 $1 coins. Circulating 1999 $1 coins are generally poorly-struck too, with the Queen's face almost always being indistinct.
Both the small and medium obverses were used on the non-circulating Last ANZACs $1 coins as well. There is no reported usage of the large head obverse on the Last ANZACs dollars (Andrews, http://thesandpit.net/index.php?option=1999dollar) lending more credence to the theory it is not a distinct variety.