IIRC, the union described the flaws of the list. It wasn't a test as much as it was a survey. MLB wanted an idea of how many people were using. There weren't definite tests, as MLB wanted a loose understanding rather than an exact number. They also said there were more names than positive test results. I thought it was kinda well known, I guess not, I'll see if I can find the statement.
Also - I understand there is bias for the MLBPA to protect it's players, but there wasn't a strong rebuttal to this statement by any particular party.