The clones that are against the 3' UTR of the target are included so one could rescue the knockdown phenotype with the introduction of a cDNA clone corresponding to the target. Transcripts from an exogenous cDNA clone would not be susceptible to silencing compared to the endogenous copy. Many publications/review committees require such an experiment to verify the observed phenotype. However, while most target sets have this added feature, not all target sets have a 3' UTR clone.