2001 Australian dollar varieties
The Ian Rank-Broadley obverse underwent a number of changes during its use on Australian decimal coins. One of the more obvious changes was the change to the spacing of the initials IRB in 2001.
The 2001 $1 coin was struck with two obverse designs. On the first the initials IRB under the Queen's neck are spaced and in a sans serif font. On the second the initials IRB under the Queen's neck are joined and in a serif font.
A number of different $1 were produced in 2001 - the Centenary of Federation design which circulated; the Volunteers design which circulated; the Australian Army anniversary design which did not circulate; the Australian Navy anniversary design which did not circulate and the Australian Air Force anniversary design which did not circulate.
Among the circulating designs, the IRB joined obverse appears to have been used on all circulating Centenary of Federation and Volunteer coins. The IRB spaced obverse is also known on Centenary of Federation coins in mint sets, but it probably was not used for circulating coin. The author has found an IRB spaced Centenary of Federation coin in circulation though it is possibly from a set.
Among the non-circulating designs, the Australian Army anniversary, the Australian Navy anniversary and the Australian Air Force anniversary coins are all known with the IRB joined design. McDonald reports that Australian Army anniversary coins are also known with the IRB spaced design (p172, McDonald, Pocket Guide to Australian Coins and Banknotes, 2017) though it is the less common variety.
Most 2001 Australian $1 were struck with the IRB joined obverse so it seems that the IRB spaced obverse had a very short life - probably being phased out in 2000 during mint set production.