You know this may have nothing to do with anything but in many episodes from the first 3 seasons there were various technical goofs such as boom mic shadows and even some studio noises.
Perhaps devices or whatever.
The episodes where Betty goes to pick up balloons and tries to come in the big window that didn't exist later on.
Shortly after she entered just before seeing the actual mic there's a sound of something probably connected to the equipment.
I wonder if some of the editing in seasons 2 and 3 may have been because of such things but them more likely not since we can plainly see then on Amazon or
www.misterrogers.org/ With perhaps the PP films I wonder if any royalty issues may had forced any edditing later on?