Koss wrote:Only one set can be right
I don't think that is correct.
By way of analogy, if you were creating these filters in hardware as capacitor-resistor networks, there are many alternative choices of values to produce the required filter. The important thing is that the set of values used produces the required result. High order IIR filters are usually produced by cascading multiple low order feedback delay filters. An error at one level of the cascade will be compounded by subsequent levels of the cascade. Alternatively, the subsequent levels of the cascade can be tweaked to compensate for errors higher up the cascade, so that the overall result is better than using the "right" values. The situation is not a bad for digital filters as for traditional analogue filters because we are not limited by choices of standard component values, but we still don't have infinite precision.
The big question is: "Do the Nyquist filters produce the right results?"
Some years ago I noticed this difference from the usual quoted values, so I tested the filters, and was pleasantly surprised by how close they model "ideal" filters.
It's all open source, so you are free to hack the code and substitute the "correct" values, then compare the results with what Nyquist uses. I expect that the result will be very similar, but not quite as good.