Interesting. I never heard that before. As stated earlier alot of old golf clubs, such as McGregor Hogan Parmasters were made of forged stainless steel. I have always thought that forged form stainless is ideal for clubs including putters. I thought the 2000 Australians were stainless. Do you have a verified reference for the nickel? I'll stand corrected. The A10s were said to be made of cast stainless steel. Stainless steel is a term that refers to many types of steel that tends not to rust. I rarely to never see rust on the Australian Blade 2000. It could be that particular steel had high levels of nickel and chrome. Chrome is the main component of most stainless steels that provide the rustless quality. It is possible that the Baldes were cast. I would have made the nickel chrome steel forged for better feel and toned down the roll marks.
It has not been stated yet what type of cast or form forging was applied to the 2000 Australian blades.
https://mizunogolf.com/ca/art-of-forging/
"In general, form forged are rough cast, then pounded into final shape with a forging process. Full on forged is pounded into shape from a billet of steel."