The Statement 1 apparently had a rated output of 0.5 mv. My suspicion is that the reference to 0.5 mv in the description of the Statement 2 is simply a mistake, perhaps the result of the person who created the description of the Statement 2 doing that by working from the description of the Statement 1. Or perhaps the description of the Statement 2 was written early in its development, when it might have been anticipated that it would have an output similar to the Statement 1, but in the end it turned out to be a 1 mv cartridge.
But yes, in many cases Grado has over the years offered both low output and high output cartridges under the same model designation. Although in most or all of those cases the high output version has been rated considerably higher than 1 mv., and the low output version considerably lower than 1 mv.
Regards,
-- Al