In recent days I've read at least two versions as to which whistle is presently on the engine.

One states it's the whistle she was wearing when she was donated to the Pomona group in 1961.
That would make sense, since the whistle came with her from Pomona to Cheyenne and was blown on air during the course of that trip.

The other day, somebody was claiming that it was the whistle previously used on 844.

The bottom line is that whistles were swapped on locomotives throughout their service lives. If one came in the shop with a bad whistle, one came off the supply shelf. This could have been a newly manufactured spare or a rebuilt one off another locomotive.

None of U.P.'s big three have the whistles they left the ALCo plant with.

All of the Big Boys, both the little and big Challengers and the FEFs all carried Hancock 3-Chime whistles. These were off-the-shelf whistles, not custom U.P. whistles. That's 175 engines with the same model whistle. There were two versions of this whistle, but they both sounded the same musical notes A-C-E. The earlier version had a flat top and the later model was a step-top. The 1936 Challengers and the FEF-1 and FEF-2 classes of 800s had the flat top as delivered. The rest were delivered with the step-top version.

For what it's worth 4449 and 611 and hundreds of other engines on many railroads had the same whistles. There are many reasons that they don't all sound exactly alike.

If you want to hear how drastically different these whistles could sound, check out these recordings on U.P.'s website.

It's shouldn't surprise anyone that the whistles could and did sound different. They are not precision musical instruments, after all. Even modern air horns can get out of pitch or have one or more of their chimes not sound at all.

A couple of years ago a big deal was made about how 4449 had received an "original Daylight whistle" to replace the "Northern Pacific Challenger whistle" she had carried for a long time. Seems nobody bothered to point out that both whistles were Hancock Long Bell 3-chimes.