What's the dyno test? How did the vehicle go 491 miles on a charge? That's great.The 491 is the actual result achieved on the dyno test.
Numbers are "derated" by a standard 30% (multiply x .7) to better reflect real world results.
If the manufacturer elects to use the 5-cycle test, they can apply a different value with sufficient documentation. Rivian uses 28% for the R1T and 30% for the R1S from the raw (unadjusted) test results.