Not all 237 occurrences fall in quotations of the Hebrew Scriptures. The New World Translation's Appendix C3 lists the remaining verses, which “do not contain either a direct or an indirect quotation from the ‘Old Testament’ that uses the Tetragrammaton” and where the name is supplied on contextual grounds.

“These verses do not contain either a direct or an indirect quotation from the “Old Testament” that uses the Tetragrammaton. However, there are either strong contextual grounds or linguistic reasons for restoring the divine name in these verses. … It should be noted, though, that the New World Bible Translation Committee did not rely on these translations as the basis for restoring the divine name in the Christian Greek Scriptures.”

“Today, however, no manuscripts of the “New Testament” from the first century C.E. are available for us to examine. So no one can check the original Greek manuscripts of the “New Testament” to see whether the Bible writers used the Tetragrammaton. The Greek manuscripts of the “New Testament” that would have a bearing on this issue are copies that were made from about 200 C.E. onward.”