Do irons shafts take time to run-in?

Hi peeps,

Just wondering on a point. Do the steel shafts on irons actually take some time and 100-200 balls to actually run-in and flex to its actual expected performance like how driver shafts do?

Cos i tried two sets of irons (one is brand new and the other is seasoned) on the same exact shaft, but somehow the brand new one feels stiffer and dead (like the shaft hasn't sort of come to life) and its acquired distance on the same club is lesser.

Also, the older set is Mp53, and the newer one is 68. Am i supposed to be expecting differences given the fact that one is CB while one is MB? Thanks for the enlightenment!