Two points:
The 01. Dec. 2004 [?] Watchtower made reference to Jason BeDuhn's book Truth in Translation &c, which they claimed gave a favourable review of the New World Translation. And it did. However, in the Appendix it also included a (scathing) consideration of the interpolation of the word "Jehovah" in the New Testament. I guess the Society's scholars didn't read to the end of the book...
The Society also admitted to altering the New Testament. The Forward of the 1981 Englisch Edition of the New World Translation states on page 6: "An effort was put forth to bring about even greater consistency in the renderings of the related parts of the Holy Scriptures, such as in harmonizing with the original Hebrew readings the readings of quotations made in the Christian Greek Scriptures." This despite the fact that such quotations are often demonstrably taken verbatim from the Septuaginta -- NOT from the Hebrew text of the Old Testament.