Location: Pretoria, South Africa (currently Fort Collins, CO)
Age: 43
Posts: 53
The International Orchid Register can be accessed on the Royal Horticultural Society's website (here) for just such questions.
Curiously, they list two separate entires for Slc. Anzac! There's one registered in 1915 as Sc. Bletchleyensis x Sc. Clive Lawrence, and another one registered in 1921 as Sc. Marathon x Sc. Dominiana, as littlefrog pointed out.
Any idea why there would be two kinds of crosses carrying this epithet?