It does mean that when the conductor has a wet and a dry rating, and that is way I qualified my comment with "for this insulation type".I thought the -2 suffix meant the dry temperature rating also applies in wet applications.
RHW only has a single rating of 75?C for both wet and dry locations. RHW-2 has a single rating of 90?C for both wet an dry locations. Now if you look at THW, you will find that it has a wet location rating of 75?C and and a dry location rating of 90?C. The addition of the "-2" to the THW does mean that it has a 90?C rating for both wet and dry locations.