The NIV study Bible provides a much more down to earth explanation for this than the WT.
Note on Mat 1:5 " since quite a long time had elased between Rahab and David and because of Matthews desire for systematic organisation many of the generations between these two ancestors were assumed , but not listed , by Matthew . "
Note on 1: 7 " fourteen generations ...... fourteen .......fourteen . These divisions reflect two characteristics of Matthews gospel 1 an apparent fondness for numbers . 2 concern for systematic arrangement . The number fourteen may have been chosen because it is twice the number 7 ( the number of completeness ) and / or because it is the numerical value of the name David . For the practise of telescoping genealogies to achieve the desired number of names see Introduction to 1 Chronicles "
The introduction to 1 Chron is a bit long , but basically explains that genealogies had different functions , so one drawn up to establish a right of inheritance would only name the ancestors that had a bearing on that right
It was not unusual for genealogies to be telescoped both inside and outside of the Bible .
" The most common type of fluidity in Biblical materials is telescoping , the omission of names from the list . Unimportant names are left out in order to relate an individual to a prominant ancestor , or possibly to achieve the desired number of names in the genealogy "
What I don't understand is how the "experts " at the WT didn't know this !!!!!