There have been numerous incidents where the Lakewood Shatnez test under the hashgocha of the Lakewood Bais Din L'Inyanay Shatnez, has been found to be definite Shatnez even though it was certified as Non-Shatnez.
The incidents were numerous, too many to be called a mistake. The places where the Shatnez was fond indicate a complete lack of knowledge of the expertise required to properly check for Shatnez.
Therefore previous tested clothing by above, should be re-tested by a qualified test center.
The fact of the Bais Din certification on that Test center puts to question of the Knowledge the Members of the Bais Din poses in the Expertise of Shatnez testing.
The Lakewood Test center, is an offspring of the Monsey test Center, which has been proven on numerous occasions not to have the basic knowledge required for testing.
Therefore one should only utilize a shatnez testing lab certified by "The International Association of Shatnez testers". There are currently 3 certified "reliable" test centers in lakewood.