Per the VEX website, the expected dimensions for VEX IQ rubber bands are as follows:
Rubber Band #32 (275-1089)
- Length: 3" (76 mm)
- Width: 1/8" (3 mm)
- Thickness: 1/32" (0.8 mm)
Rubber Band #64 (276-3990)
- Length: 3.5" (89 mm)
- Width: 1/4" (6 mm)
- Thickness: 1/32" (0.8 mm)
Although it is tough to tell, it appears that the rubber band in the attached image meets the nominal dimensions for a #64 size, and would therefore be legal.
In general, the reason why rubber band sizes are referred to in nominal terms (e.g. #32, #64) is because it is impossible to guarantee a rubber band's exact dimensions with 100% certainty. Rubber may expand or contract due to temperature, humidity, repeated over-stretching, etc. If students are raising concerns about the legality of their official VEX rubber bands, this could serve as a "teaching moment" to explain material properties, tolerances, etc.
The intent of R8-c is to clarify that although off-the-shelf rubber bands are permitted, searching for "the perfect rubber band" should not be a part of the design challenge. Inspectors may request measurements of rubber bands that appear to be grossly outside of the expected sizes, but measuring to millimeter precision should not be necessary.