I would place the responsibility on the manufacturer to explain/demonstrate to their clients what is different between the former version and an upgraded or updated version.
I place the responsibility on the reviewer to,
- At a minimum, use partnering equipment that would reasonably be expected to be used with the review equipment - i.e., no mis-matches, and to
- Compare the reviewed equipment with comparable competitors available in the market at the time of the review.
I was fortunate to have seen reviews by the same reviewer, of my new DAC and of the same manufacturer’s former DAC. The direct comparisons were certainly helpful in knowing what I should expect. However, that will mostly not be practical, as several here have pointed out. 6moons usually does a good job of making meaningful comparisons, IMO.