They might be similar to Intel's "S-Spec" number, to keep track of processor revisions? Not 100% sure either. Anyways, they're not in the model designation at all but part of the order part number.

Rikintosh wrote on 2024-02-07, 21:59:

AFX, AFR, AHX...

Oh boy, ever heard of google.com?

https://en.wikipedia.org/wiki/List_of_AMD_K6_processors

EDIT:
found that only in German quickly
https://de.wikipedia.org/wiki/Ordering_Part_N … AMD-Prozessoren
so the last letter:
K = 0 °C to 80 °C
Q = 0 °C to 60 °C
R = 0 °C to 70 °C
X = 0 °C to 65 °C
Z = 0 °C to 85 °C

For K6-2/K6-III parts:
First letter - Package Type (A = 321-pin PGA, B = 360-pin BGA, I = 349-pin BGA)
Second letter - Operating Voltage (U = 1.4V - 1.6V, T = 1.5V - 1.7V, P = 1.6V - 1.8V, N = 1.7V - 1.9V, M = 1.8V - 2.0V, C = 1.9V-2.1V, D = 2.0V - 2.2V, F = 2.1V - 2.3V, G = 2.2V - 2.4V, H = 2.3V - 2.5V)
Third letter - Case Temperature (Q = 0 - 60C, X = 0 - 65C, R = 0 - 70C, K = 0 - 80C, Z = 0 - 85C)