It doesn't hurt the credibility of the stat itself, and i will explain why. WAR is a statistic that is based on past performance. When importing data from another league, there is a significant margin for error which the creator/applicator of the stat freely acknowledges. In this case, it is merely an attempt to project what a player might do, so they can set a benchmark approaching how teams as a whole could do, besides rating possible individual performances. This is not the regular use of the stat, and should not be considered so, but it's the best thing we've got when trying to even ballpark what Castillo might do.