Your EC should have advised of works in the stairwell as this would presumably affect access to your complex. It may well have been necessary to tile the area as removing the mowings might have damaged surrounding tiles. I would think this would be a repair. You wouldn’t want anyone tripping and injuring themselves on common property.
I would have thought that it would be necessary to have a by law drawn up stipulating that the windows were now considered an owners responsibility. Passing a motion that owners have two years to replace their windows doesn’t take into consideration future owners should they have problems with their window frames. If someone moves into the complex in three or four years and they have a problem with their windows, where is it written that owners are responsible for their repair/replacement?