That's not a useful metric. The questions that today show up as locked for historical significance were simply closed before the historical significance lock was introduced.
Conversely, the lock was introduced to stop those highly interesting (but ultimately useless) questions from getting deleted. If anything, it's a step in being less strict.
Conversely, the lock was introduced to stop those highly interesting (but ultimately useless) questions from getting deleted. If anything, it's a step in being less strict.