Most of the fine wire I have come across start life with only one wire.
Never really gave much thought to the rare event of cracking in the fine wire plugs before, but during my appy time the entire large fleet of piston twins used fine wire and the plug washers were all annealed. So I am pretty sure that is not a reason.
I have always torqued spark plugs to the correct torque and they are mostly the champion breed.
Thinking about it more cracking on massive electrodes was not as common as it is now, I would guess it around 4 times more common now.
So I doubt old pilots have changed operation much if at all in many cases and the engines are the same. I still clean and test them the same.
I think the spark plug (material/process) itself maybe a large factor - I don't think it is the fuel as the green and blue from memory was no noticeable difference in cracks.