Romane, tak Tvoji teorii na IMDB nikdo nepotvrdil ale asi to bude tím, že oni mají inche :-)))
Každopádně je tam pár zajímavých úvah:

*If they met in the 1963, reunited in 1967 and Jack died in 1983 (at least he does in the book, not so sure about the film) then the year of the trailer scene is 1984, cos its meant to be a year later. 1984, thats 17 YEARS since they were reunited.

*refer enced Chinese symbology that the number 8 represents Rebirth. There are other symbols of new life in that scene as well: Alma, Jr.'s, impending marriage, Ennis's newly awakened sense of the importance of making sacrifices for loved ones, and the view of the young green crops seen from the window in the last shot

*The numbers 1 and 7 on Ennis' mail box, when turned upside down, read L and I, Li, which is the phonetic spelling for Lee! It can't be a coincidence!
Not only that, but LI in Roman numerals equals 51, which is Lee's age!!!

*somebody mentioned the clock in Jack's bedroom, which has stopped at 8:45. 8+4+5=17

*Someon e else mentioned that the 17 letter of the alphabet is "Q" , could represent Ennis' acceptance of his nature

*"17 inches, the size of the monitor I'm viewing this right now

*I don't think Ennis had any thought or power of his own to number his mailbox "17", because the address shall be given by authorities of this camping park or range owner.
Putting the number on the mailbox would be shown that Ennis either has just moved in or Ennis decided to open up his life to have contact with outside world.