Different whistles. The one on 484 and 497 was a worn out Reading 6-chime, that when it was healthy sounded a lot like the 6-chime 493 was running with until recently.
The whistle the 484 had in the mid-late 1970's it the one I was referring to. It was a standard D&RGW 5-chime that had a casting flaw creating a hole in a couple of chimes to the central cavity where the stud from the whistle base runs up through the chime. Someone cut open the whistle chime, welded up the holes and welded it back together.
A Reading 6-chime in good shape is a great whistle. The one the C&TS needed a overhaul and a new throat plate built. They are worth a small fortune, which I'm quite sure whoever stole it was quite aware.