Legitimate Welter Weight

I got what you said, what I am trying to understand is I keep seeing post here on NSB "He did not beat a legitimate welterweight" at what weight is a illegitimate welterweight belongs to?

A fighter can't always come in a 147 on the dot because they would often be overweight. Big full sized welterweights often weigh in at 145 to 146. If they weigh in at 144 or 144.5 they are probably smaller welterweights but might still be to big to be comfortable fighting at 140. Even the biggest welterweights like Thurman often weigh in at 146 to 146.5 and then enter the ring many pounds heavier.

Is there a half-fledge welterweight?