Yeah, It's fairly well known that only professionally administered and monitored tests can be accurate at all, and multiple tests at different times gives a much more accurate average. Also, as your performance on any test is subject to many factors, it's best to see any given score as just a "snapshot" of you at one time, on one day. That isn't to say, however, anyone can discount a score of, say, 145 as just it having been "a good day," and likewise a very low score can't be refuted as not being at least mostly accurate.