If memory serves, older process technologies are intrinsically a little more rad-hard, just because a 1um 6T cell is roughly a hundred times larger than a 14nm

If memory serves, older process technologies are intrinsically a little more rad-hard, just because a 1um 6T cell is roughly a hundred times larger than a 14nm 6T cell... (giving it greater drive strength and larger "ballast parasitics" to absorb radiation events) They probably built them with a lot more margin back then too.