This is what NWEA MAP has on their web site about triangulating data and it should apply to all assessments:
NWEA assessments and the resulting scores are among the most valid and reliable information available to educators. Nevertheless, no single instrument or data point should ever be used when making significant educational decisions about a student. In these situations, NWEA recommends using the principle of triangulation.
Triangulation is simply the process of using three points of data that say the same thing about a student when making educational decisions about that student. Any single assessment score - be it from MAP or any other assessment - is subject to environmental or motivational influences which can affect its accuracy. If a student is suffering from ill health or emotional stress which detract from their ability to perform to the best of their ability, that particular test data may be invalid. Likewise, if a student is resistant to the idea of testing, they may intentionally sabotage the test results by answering in a random or intentionally incorrect manner.
School personnel have a wealth of data available about their students, ranging from teacher-made tests and observations to periodic test results (like MAP), to state mandated assessments. Add to this the input from previous teachers, parents, and school records, and it is easy to see that obtaining a "body of evidence" regarding a student's educational status is well within the reach of school staff.
NWEA's assessment scores and the associated reports and resources provided are extremely useful tools for informing instruction in the classroom, but they should not be used in exclusion to other data sources. Using triangulation assures that the most informed and appropriate decisions are being made in behalf of each student.http://www.nwea.org/support/article/528/triangulation-data